docs: fix ADVANCED_FEATURES and REST_API_REFERENCE

REST_API_REFERENCE.md
- Wrong path: /fonts/delete/<font_family> -> /fonts/<font_family>
  (verified the real DELETE route in
  web_interface/blueprints/api_v3.py).
- Diffed the documented routes against the real api_v3 blueprint
  (92 routes vs the 71 documented). Added missing sections:
  - Error tracking (/errors/summary, /errors/plugin/<id>, /errors/clear)
  - Health (/health)
  - Schedule dim/power (/config/dim-schedule GET/POST)
  - Plugin-specific endpoints (calendar/list-calendars,
    of-the-day/json/upload+delete, plugins/<id>/static/<path>)
  - Starlark Apps (12 endpoints: status, install-pixlet, apps CRUD,
    repository browse/install, upload)
  - Font preview (/fonts/preview)
- Updated table of contents with the new sections.
- Added a footer note that the API blueprint mounts at /api/v3
  (app.py:144) and that SSE stream endpoints are defined directly on
  the Flask app at app.py:607-615.

ADVANCED_FEATURES.md
- Vegas Scroll Mode section was actually accurate (verified all
  config keys match src/vegas_mode/config.py:15-30).

- On-Demand Display section had multiple bugs:
  - 5 occurrences of port 5050 -> 5000
  - All API paths missing /v3 (e.g. /api/display/on-demand/start
    should be /api/v3/display/on-demand/start)
  - "Settings -> Plugin Management -> Show Now Button" UI flow doesn't
    exist. Real flow: open the plugin's tab in the second nav row,
    click Run On-Demand / Stop On-Demand.
  - "Python API Methods" section showed
    controller.show_on_demand() / clear_on_demand() /
    is_on_demand_active() / get_on_demand_info() — none of these
    methods exist on DisplayController. The on-demand machinery is
    all internal (_set_on_demand_*, _activate_on_demand, etc) and
    is driven through the cache_manager. Replaced the section with
    a note pointing to the REST API.
  - All Use Case Examples used the same fictional Python calls.
    Replaced with curl examples against the real API.

- Cache Management section claimed "On-demand display uses Redis cache
  keys". LEDMatrix doesn't use Redis — verified with grep that
  src/cache_manager.py has no redis import. The cache is file-based,
  managed by CacheManager (file at /var/cache/ledmatrix/ or fallback
  paths). Rewrote the manual recovery section:
  - Removed redis-cli commands
  - Replaced cache.delete() Python calls with cache.clear_cache()
    (the real public method per the same bug already flagged in
    PLUGIN_API_REFERENCE.md)
  - Replaced "Settings -> Cache Management" with the real Cache tab
  - Documented the actual cache directory candidates

- Background Data Service section:
  - Used "nfl_scoreboard" as the plugin id in the example.
    The real plugin is "football-scoreboard" (handles both NFL and
    NCAA). Fixed.
  - "Implementation Status: Phase 1 NFL only / Phase 2 planned"
    section was severely outdated. The background service is now
    used by all sports scoreboards (football, hockey, baseball,
    basketball, soccer, lacrosse, F1, UFC), the odds ticker, and
    the leaderboard plugin. Replaced with a current "Plugins using
    the background service" note.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/REST_API_REFERENCE.md

@@ -24,6 +24,17 @@ All endpoints return JSON responses with a standard format:
 - [Cache](#cache)
 - [WiFi](#wifi)
 - [Streams](#streams)
+- [Logs](#logs)
+- [Error tracking](#error-tracking)
+- [Health](#health)
+- [Schedule (dim/power)](#schedule-dimpower)
+- [Plugin-specific endpoints](#plugin-specific-endpoints)
+- [Starlark Apps](#starlark-apps)
+
+> The API blueprint is mounted at `/api/v3` (`web_interface/app.py:144`).
+> SSE stream endpoints (`/api/v3/stream/*`) are defined directly on the
+> Flask app at `app.py:607-615`. There are about 92 routes total — see
+> `web_interface/blueprints/api_v3.py` for the canonical list.
 
 ---
 
@@ -1201,10 +1212,16 @@ Upload a custom font file.
 
 ### Delete Font
 
-**DELETE** `/api/v3/fonts/delete/<font_family>`
+**DELETE** `/api/v3/fonts/<font_family>`
 
 Delete an uploaded font.
 
+### Font Preview
+
+**GET** `/api/v3/fonts/preview?family=<font_family>&text=<sample>`
+
+Render a small preview image of a font for use in the web UI font picker.
+
 ---
 
 ## Cache
@@ -1439,6 +1456,130 @@ Get recent log entries.
 
 ---
 
+## Error tracking
+
+### Get Error Summary
+
+**GET** `/api/v3/errors/summary`
+
+Aggregated counts of recent errors across all plugins and core
+components, used by the web UI's error indicator.
+
+### Get Plugin Errors
+
+**GET** `/api/v3/errors/plugin/<plugin_id>`
+
+Recent errors for a specific plugin.
+
+### Clear Errors
+
+**POST** `/api/v3/errors/clear`
+
+Clear the in-memory error aggregator.
+
+---
+
+## Health
+
+### Health Check
+
+**GET** `/api/v3/health`
+
+Lightweight liveness check used by the WiFi monitor and external
+monitoring tools.
+
+---
+
+## Schedule (dim/power)
+
+### Get Dim Schedule
+
+**GET** `/api/v3/config/dim-schedule`
+
+Read the dim/power schedule that automatically reduces brightness or
+turns the display off at configured times.
+
+### Update Dim Schedule
+
+**POST** `/api/v3/config/dim-schedule`
+
+Update the dim schedule. Body matches the structure returned by GET.
+
+---
+
+## Plugin-specific endpoints
+
+A handful of endpoints belong to individual built-in or shipped plugins.
+
+### Calendar
+
+**GET** `/api/v3/plugins/calendar/list-calendars`
+
+List the calendars available on the authenticated Google account.
+Used by the calendar plugin's config UI.
+
+### Of The Day
+
+**POST** `/api/v3/plugins/of-the-day/json/upload`
+
+Upload a JSON data file for the Of-The-Day plugin's category data.
+
+**POST** `/api/v3/plugins/of-the-day/json/delete`
+
+Delete a previously uploaded Of-The-Day data file.
+
+### Plugin Static Assets
+
+**GET** `/api/v3/plugins/<plugin_id>/static/<path:file_path>`
+
+Serve a static asset (image, font, etc.) from a plugin's directory.
+Used internally by the web UI to render plugin previews and icons.
+
+---
+
+## Starlark Apps
+
+The Starlark plugin lets you run [Tronbyt](https://github.com/tronbyt/apps)
+Starlark apps on the matrix. These endpoints expose its UI.
+
+### Status
+
+**GET** `/api/v3/starlark/status`
+
+Returns whether the Pixlet binary is installed and the Starlark plugin
+is operational.
+
+### Install Pixlet
+
+**POST** `/api/v3/starlark/install-pixlet`
+
+Download and install the Pixlet binary on the Pi.
+
+### Apps
+
+**GET** `/api/v3/starlark/apps` — list installed Starlark apps
+**GET** `/api/v3/starlark/apps/<app_id>` — get app details
+**DELETE** `/api/v3/starlark/apps/<app_id>` — uninstall an app
+**GET** `/api/v3/starlark/apps/<app_id>/config` — get app config schema
+**PUT** `/api/v3/starlark/apps/<app_id>/config` — update app config
+**POST** `/api/v3/starlark/apps/<app_id>/render` — render app to a frame
+**POST** `/api/v3/starlark/apps/<app_id>/toggle` — enable/disable app
+
+### Repository (Tronbyt community apps)
+
+**GET** `/api/v3/starlark/repository/categories` — browse categories
+**GET** `/api/v3/starlark/repository/browse?category=<cat>` — browse apps
+**POST** `/api/v3/starlark/repository/install` — install an app from the
+community repository
+
+### Upload custom app
+
+**POST** `/api/v3/starlark/upload`
+
+Upload a custom Starlark `.star` file as a new app.
+
+---
+
 ## Error Responses
 
 All endpoints may return error responses in the following format: