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>

web_interface/blueprints/api_v3/plugins.py

@@ -153,6 +153,9 @@ def get_installed_plugins():
             'category': plugin_info.get('category', 'General'),
             'description': plugin_info.get('description', 'No description available'),
             'tags': plugin_info.get('tags', []),
+            # The tab nav uses this as the <i> element's Font Awesome class
+            # (app-shell.js / app-early.js); only a string can be one.
+            'icon': plugin_info.get('icon') if isinstance(plugin_info.get('icon'), str) else None,
             'enabled': enabled,
             'verified': verified,
             'loaded': plugin_info.get('loaded', False),