refactor: remove the skin system and the unused src/base_classes package (#615)

* refactor: remove the skin system

Skins never rendered with the current scoreboard plugins: the only hook was
SportsCore._render_game in src/base_classes, which no plugin builds on, so
the UI and store already treated them as unsupported. The owner decided on
2026-09-23 to remove them outright.

Removed src/skin_system/ (runtime, base class, fixtures), skins/,
scripts/validate_skin.py and their tests; the store's "type": "skin"
installer, uninstaller and hide/refuse filters (the official registry lists
no skins); SchemaManager.inject_skin_selector; and GET /api/v3/skins.

Stored skin/skin_options config values are handled in the next commit.

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

* fix(config): drop retired skin/skin_options keys instead of validating them

A config.json written while the skin system existed can carry skin and
skin_options in any plugin section, and most plugin schemas set
additionalProperties: false. They are no longer core plugin properties;
RETIRED_PLUGIN_KEYS in schema_manager lists them and
drop_retired_plugin_keys removes them (unless the plugin's own schema
declares the name) in prepare_plugin_config, which loading, hot reload,
GET /plugins/config and both web saves already share, and in
validate_config_against_schema for callers that validate a raw section.
POST /plugins/config and /config/main also drop them from the stored
section they merge into, so they leave config.json on the next save.

Tests cover the load path (real PluginManager.load_plugin: no schema
warning, not degraded), raw and prepared validation,
validate_all_plugin_configs, and the JSON, form and /config/main saves.

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

* refactor: remove the unused src/base_classes package

No scoreboard plugin builds on src.base_classes: the nine monorepo
scoreboards ship their own sports.py and share code through src/common
(docs/SPORTS_UNIFICATION.md), and none of the third-party registry plugins
imports it. The one import anywhere, baseball-scoreboard's
rankings_manager.py, is a lazy import of ESPNDataSource in a class nothing
instantiates.

Removed the package and the eight test files that only tested it
(test_api_extractors, test_data_sources, test_sports_base_characterization,
test_sports_capabilities, test_sports_core_promotions,
test_sports_logo_cache_bounded, test_sports_modes_promotions,
test_sports_odds_fanout). test_common_is_hardware_free no longer lists
src.base_classes as a forbidden import, and comments in sports_helpers.py
and base_odds_manager.py stop pointing at it.

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

* docs: drop the skin system and src/base_classes from the docs

Deletes docs/SKIN_SYSTEM.md and docs/CREATING_SKINS.md and every link to
them (docs/README.md, README.md, PLUGIN_DEVELOPMENT_GUIDE.md, the /skins
section of REST_API_REFERENCE.md), the skin section of CLAUDE.md and the
term in PRODUCT.md. SPORTS_UNIFICATION.md now says src/base_classes was
removed and shared code lives in src/common, in the Layering section and
the view-model-contract rule. Other docs stop pointing at the removed
package. CHANGELOG records both removals under Unreleased.

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

* fix(store): hide and refuse registry entries that aren't plugins

The skin filters went with the skin system, but a custom registry can still
list "type": "skin" entries, and installing one as a plugin would unpack it
into the plugins directory. PluginStoreManager.is_plugin_entry() (a missing
type means plugin) now hides non-plugin entries from the store and
custom-registry listings, and install refuses them, in the route with a
clear 400 and in _install_plugin_impl for any other caller.

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

---------

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

CLAUDE.md

@@ -45,17 +45,6 @@
 - Plugin configs stored in `config/config.json`, NOT in plugin directories — safe across reinstalls
 - Third-party plugins can use their own repo URL with empty `plugin_path`
 
-## Skin System (visual overlays for sports scoreboards) — NOT SUPPORTED YET
-- Skins do not render with the current scoreboard plugins: the only hook is `SportsCore._render_game()` in `src/base_classes/sports/core.py`, and no current scoreboard plugin (monorepo or third-party registry) builds on `src.base_classes`
-- So core doesn't offer them: no Visual Skin dropdown (`get_plugin_schema` skips `inject_skin_selector`), the store hides/refuses `"type": "skin"` entries, `GET /api/v3/skins` reports `"supported": false`. Switch: `SKINS_RENDER_SUPPORTED` in `src/skin_system/__init__.py`
-- Stored `skin` / `skin_options` config values must keep loading and saving (base schema allows them; form saves deep-merge over the stored section)
-- Skins live in `skins/<skin-id>/` (skin.json + skin.py), NOT in plugin dirs — plugin reinstall deletes plugin dirs
-- Core: `src/skin_system/` (ScoreboardSkin, SkinContext, runtime); keep it and its tests
-- Skins render onto `ctx.canvas` only; fallback to built-in renderer on `False`/exception (3 strikes disables for session)
-- View-model guaranteed keys are frozen (see `test/test_skin_system.py::TestViewModelContract`) — renaming keys in `_extract_game_details_common` or sport extractors breaks published skins
-- Validate skins headlessly: `python scripts/validate_skin.py --skin <id>`; docs: `docs/SKIN_SYSTEM.md`, `docs/CREATING_SKINS.md`
-- Skins are NOT monorepo plugins: no manifest bump / update_registry.py needed
-
 ## Common Pitfalls
 - paho-mqtt 2.x needs `callback_api_version=mqtt.CallbackAPIVersion.VERSION1` for v1 compat
 - BasePlugin uses `get_logger()` from `src.logging_config`, not standard `logging.getLogger()`