fix: web UI and src.common bugs (wifi wrong-password, plugin icon, starlark toggle, API caching, scroll/logo/font helpers) (#646)

- wifi: keep the "wrong_password:" prefix through the restore/AP fallback so
  the UI's incorrect-password prompt fires again.
- /plugins/installed returns the manifest's icon (string only).
- /starlark/apps/<id>/toggle coerces `enabled` and delegates to
  _toggle_starlark_app (disk before memory, no KeyError, "false" is false).
- /api/v3/ JSON GETs are sent Cache-Control: no-store; non-JSON keeps 5s.
- ScrollHelper.set_scrolling_image converts non-RGB input (alpha onto black);
  create/set_scrolling_image reset last_update_time like reset_scroll.
- LogoHelper backs off a failed download per path for
  MISSING_LOGO_RECHECK_SECONDS; cleared on invalidate/clear_cache.
- refresh_placeholder_timestamp saves atomically.
- FontManager.clear_cache / _clear_plugin_font_cache bump cache_generation.
- Odds manager: per-game logs to DEBUG; JSON decode error caught before
  RequestException (same cooldown).
- element_style mangled continuations; startup validator skips null plugin
  blocks and reuses the controller's discovery.
- src/common/README lists frame_timing, json_body, render_gate.

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

docs/PLUGIN_CUSTOM_ICONS.md

@@ -5,11 +5,9 @@
 A plugin can name an icon for its tab in the web interface's second nav row
 (next to **Plugin Manager**) with the `icon` field in `manifest.json`.
 
-> **Status:** the tab code honors `icon`, but `GET /api/v3/plugins/installed`
-> (`web_interface/blueprints/api_v3/plugins.py`) does not currently include
-> the manifest's `icon` in its response, so every tab shows the default
-> puzzle piece. Setting `icon` is harmless and will take effect once the API
-> passes it through again.
+`GET /api/v3/plugins/installed` passes the manifest's `icon` through (a
+non-string value comes back as `null`), and a plugin without one gets the
+default puzzle piece.
 
 ## Font Awesome classes only
 
@@ -55,8 +53,8 @@ With no `icon` (or an empty one) the tab shows `fas fa-puzzle-piece`.
    or misspelled class renders as a blank space.
 2. Include the style prefix (`fas`, `far` or `fab`) as well as the icon
    class.
-3. See the status note above: the icon is currently not passed through by
-   the API.
+3. The manifest is re-read on each plugin list load; reload the page after
+   editing `icon`.
 
 ## Related Documentation