refactor: delete dead Python code in the core (and stop storing Wi-Fi passwords) (#608)

* refactor(plugins): remove the no-op PluginHealthMonitor

Its monitor loop did nothing (`if callbacks: pass`), register_health_check
had no callers and api_v3.health_monitor was never read by any route. The
live health data comes from PluginHealthTracker, which is untouched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(store): drop the never-set uninstall tombstones

Nothing in production called mark_recently_uninstalled, so the
reconciler's was_recently_uninstalled check was always False. The
persistent uninstall registry is what actually stops resurrection; the
reconciler test now exercises that gate instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(common): delete unused config/display/game helpers, utils and error_handler

Nothing in core, the web UI, scripts or the plugin monorepo imports
config_helper, display_helper, game_helper, utils or error_handler; only
their own tests did. The error_handler re-exports leave src.common's
__all__; APIHelper, TextHelper, ScrollHelper, LogoHelper and the adaptive
layout exports are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(config): drop ConfigService's unused versioning and save API

ConfigVersion, get_version/get_version_history/get_version_config,
rollback, save_config, reload, get_plugin_config and the backward-compat
load_config/get_config_path/get_secrets_path had no callers. The display
controller only uses get_config, subscribe, unsubscribe and shutdown,
plus the file watcher. Change detection now compares against the
current checksum instead of the last history entry.

The subscriber tests asserted `callback.called or True`; they now
reload the way the watcher does and assert the notification.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(plugins): drop unread plugin state history and callbacks

plugin_state.PluginStateManager kept a bounded per-plugin transition
history that only get_state_history (tests only) read; get_state_info
reports a separate lifetime count, which stays. set_error_info and
record_display had no callers, and set_state_with_error's `error`
argument only fed the history.

The web-side state_manager.PluginStateManager loses
subscribe_to_state_changes, _notify_callbacks, set_plugin_error and
get_state_version, none of which had callers; with no subscribers the
old-state copy in update_plugin_state went with them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(plugins): remove unused PluginManager methods and attribute guards

update_all_plugins was only called by a test (the display loop uses
run_scheduled_updates); get_plugin_health_metrics,
get_plugin_resource_metrics and get_plugin_state had no callers; and
plugin_modules was written but never read. plugin_directories is now
initialised in __init__, so the hasattr() guards around it go.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(plugins): remove unused executor, loader, store and package helpers

- PluginExecutor.execute_safe: no callers.
- PluginLoader._parse_semver: only its own tests; compatibility.parse_semver
  is the live copy and test_compatibility.py already covers it.
- PluginStoreManager.get_installed_plugin_info: no callers.
- PluginResourceMonitor._local: never read.
- src.plugin_system.get_store_manager and __api_version__: no importers in
  core, scripts or the plugin monorepo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(wifi): stop storing Wi-Fi passwords in wifi_config.json

WiFiManager appended every joined network's SSID and password, in
plaintext, to saved_networks in config/wifi_config.json, and nothing
(web UI, backup restore, scripts) ever read them back: NetworkManager
keeps its own credentials. The writes are gone, and loading the config
now drops any saved_networks key and rewrites the file, so passwords
already on disk are scrubbed.

Also removes _check_dnsmasq_conflict (never called) and _detect_trixie,
whose result only reached one log line, along with the
NM_CONNECTIONS_PATHS constant only it used.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(display): remove unreachable and unused DisplayController code

- _follower_rebuild_scroll_image: never called.
- mode_duration (never read) and last_mode_change (write-only).
- The `chosen_cap <= 0` branch: chosen_cap is either the minimum of
  caps already filtered to > 0 or DEFAULT_DYNAMIC_DURATION_CAP (180).
- The `max_duration < min_duration` branch directly after
  `max_duration = max(min_duration, max_duration)`.
- The circuit-breaker branch's `display_result = False` and
  `manager_to_display = None`: the first is overwritten a few lines
  later, the second is already None there.
- The bool-to-bool conversion of execute_display's result, which is
  always a bool.
- The `loaded_plugins` lookup in _update_modules: PluginManager has no
  such attribute, so it always fell through to `plugins`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(vegas): remove unused config update, boundary finder and refresh

VegasModeConfig.update had no callers outside its own tests (the
coordinator rebuilds the config with from_config on a change);
geometry.find_item_boundary and StreamManager._refresh_plugin_content
had no callers at all.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* refactor(run): drop the debug block that pretended to import the plugin system

In debug mode run.py put src/plugin_system itself on sys.path and printed
"Plugin system import successful" without importing anything. Nothing
imports plugin_system modules by bare name, so the path entry did
nothing either.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test: delete tests that test nothing

- test/plugins/test_{basketball_scoreboard,calendar,clock_simple,
  odds_ticker,soccer_scoreboard,text_display}.py skip everywhere the named
  plugins are not installed, including CI (LEDMATRIX_PLUGINS_DIR holds only
  the fixture plugin); test_plugin_matrix.py already covers every
  discovered plugin. Their PluginTestBase and the fixtures only it used
  (plugins_dir, mock_display_manager, mock_cache_manager,
  mock_plugin_manager, base_plugin_config in test/plugins/conftest.py) go
  with them.
- test_plugin_system.py: test_discover_plugins (body was `pass`) and
  test_dependency_check (a comment), plus the test_plugin_manager fixture
  only the former requested.
- test_display_manager.py: test_draw_image asserted that an image it had
  just assigned was not None.
- test_display_controller.py: the rotation and schedule-override tests
  re-implemented the run-loop arithmetic inline and asserted on their own
  result without calling the controller.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test: expect one plugin_last_update success stamp after update_all_plugins

EveryStampRecordsACompletion required at least two success-path stamps;
the second was update_all_plugins, removed as test-only. The worker and
synchronous paths share the remaining stamp in _execute_update_now, and
the check that every stamp calls _note_update_completed is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_vegas_config.py

@@ -2,7 +2,7 @@
 Tests for src/vegas_mode/config.py
 
 Covers VegasModeConfig: from_config, to_dict, get_frame_interval,
-is_plugin_included, get_ordered_plugins, validate, update.
+is_plugin_included, get_ordered_plugins, validate.
 """
 
 import pytest
@@ -263,48 +263,3 @@ class TestValidate:
         cfg = VegasModeConfig(scroll_speed=0.1, target_fps=5)
         errors = cfg.validate()
         assert len(errors) >= 2
-
-
-# ---------------------------------------------------------------------------
-# update
-# ---------------------------------------------------------------------------
-
-class TestUpdate:
-    def _wrap(self, **kwargs) -> dict:
-        return {"display": {"vegas_scroll": kwargs}}
-
-    def test_update_enabled(self):
-        cfg = VegasModeConfig(enabled=False)
-        cfg.update(self._wrap(enabled=True))
-        assert cfg.enabled is True
-
-    def test_update_scroll_speed(self):
-        cfg = VegasModeConfig(scroll_speed=50.0)
-        cfg.update(self._wrap(scroll_speed=90.0))
-        assert cfg.scroll_speed == 90.0
-
-    def test_update_separator_width(self):
-        cfg = VegasModeConfig(separator_width=32)
-        cfg.update(self._wrap(separator_width=8))
-        assert cfg.separator_width == 8
-
-    def test_update_plugin_order(self):
-        cfg = VegasModeConfig(plugin_order=[])
-        cfg.update(self._wrap(plugin_order=["x", "y"]))
-        assert cfg.plugin_order == ["x", "y"]
-
-    def test_update_excluded_plugins(self):
-        cfg = VegasModeConfig()
-        cfg.update(self._wrap(excluded_plugins=["skip_me"]))
-        assert "skip_me" in cfg.excluded_plugins
-
-    def test_update_ignores_missing_keys(self):
-        cfg = VegasModeConfig(scroll_speed=50.0)
-        cfg.update(self._wrap(target_fps=80))  # only fps, not speed
-        assert cfg.scroll_speed == 50.0
-        assert cfg.target_fps == 80
-
-    def test_empty_update_no_change(self):
-        cfg = VegasModeConfig(scroll_speed=50.0)
-        cfg.update({})
-        assert cfg.scroll_speed == 50.0