docs: correct semantically stale content across the user and developer guides

A second-pass content audit checked the guides' substantive claims
against the code (the first pass only fixed mechanical drift). Fixes:

- GETTING_STARTED: described booting a prebuilt SD image and seeing
  default clock/weather plugins — neither exists. Now documents the real
  install (Pi OS Lite + one-shot installer / first_time_install.sh) and
  that displays come from the Plugin Store. Duration and ordering
  instructions moved to the Rotation tab where the controls actually
  live.
- WEB_INTERFACE_GUIDE: three whole tabs were undocumented (Rotation,
  Backup & Restore, Tools) and the Display tab's Vegas Scroll section
  was unmentioned. Fonts overrides are per display element (not per
  plugin); Logs has an Auto-scroll checkbox (not a Pause button); the
  aspirational keyboard-shortcut list and no-JS claim removed.
- TROUBLESHOOTING: the hand-written service-file template (wrong user,
  wrong ExecStart, dropped the autostart gate) replaced with the real
  systemd/ units + install scripts; recovery steps no longer copy
  placeholder units verbatim; WiFi curl endpoint corrected to /api/v3/;
  cache-clearing advice now targets the real cache locations.
- ADVANCED_FEATURES: removed a false claim that CacheManager has no
  delete(); fixed two example snippets that raise TypeError
  (BackgroundDataService and get_config_file_mode signatures); fixed
  cache paths, a 5-minute TTL that is actually 1 hour, and the vegas
  table now links the complete 26-key reference.
- EMULATOR_SETUP_GUIDE: documented run.py flags that don't exist
  (--plugin/--test-plugins) removed in favor of dev_server.py and
  check_plugin.py; shipped emulator config values corrected (browser
  adapter default on :8888, not pygame).
- PLUGIN_QUICK_REFERENCE: drag-and-drop reordering is shipped, not
  'not yet supported'; discovery-fallback and registry-repo claims
  corrected. PLUGIN_API_REFERENCE: get_vegas_segment_width returns
  panels, not pixels. CONTRIBUTING: the repo uses flake8/mypy/bandit
  pre-commit hooks, not black/ruff, and tests need requirements-test.txt.
- SKIN_SYSTEM/DEVELOPER_QUICK_REFERENCE: stale module paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SXb4mKcAkVaxkeTb3YnAdr

docs/PLUGIN_QUICK_REFERENCE.md

@@ -14,8 +14,10 @@ and [PLUGIN_DEVELOPMENT_GUIDE.md](PLUGIN_DEVELOPMENT_GUIDE.md).
 ✅ **GitHub Store**: Discovery from `ledmatrix-plugins` registry plus
    any GitHub URL
 ✅ **Plugin Location**: configured by `plugin_system.plugins_directory`
-   in `config.json` (default `plugin-repos/`; the loader also searches
-   `plugins/` as a fallback)
+   in `config.json` (default `plugin-repos/`). Plugin discovery scans
+   only this directory — there is no loader fallback to `plugins/`
+   (only Plugin Store operations and schema lookup additionally probe
+   `plugins/`)
 
 ## File Structure
 
@@ -109,7 +111,7 @@ git push -u origin main
 git tag v1.0.0
 git push origin v1.0.0
 
-# Submit to registry (PR to ChuckBuilds/ledmatrix-plugin-registry)
+# Submit to registry (PR to ChuckBuilds/ledmatrix-plugins)
 ```
 
 ## Using Plugins
@@ -120,12 +122,12 @@ git push origin v1.0.0
 2. **Install**: Click **Install** in the plugin's row
 3. **Configure**: open the plugin's tab in the second nav row
 4. **Enable/Disable**: toggle switch in the **Installed Plugins** list
-5. **Reorder**: order is set by the position in `display_modes` /
-   plugin order; rearranging via drag-and-drop is not yet supported
+5. **Reorder**: use the drag-and-drop **Rotation Order** list in the
+   **Rotation** tab (saved to `display.plugin_rotation_order`)
 
 ### REST API
 
-The API is mounted at `/api/v3` (`web_interface/app.py:144`).
+The API is mounted at `/api/v3` (`web_interface/app.py:199`).
 
 ```bash
 # Install plugin from the registry