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>

src/element_style.py

@@ -840,7 +840,7 @@ def defaults_from_schema(schema: Dict[str, Any]) -> Dict[str, Any]:
                     defaults['align'] = align_spec['default']
                 scale_spec = spec.get('scale')
                 if isinstance(scale_spec, dict) and 'default' in scale_spec:
-                    layout.setdefault(element_key, {})['scale'] =                         scale_spec['default']
+                    layout.setdefault(element_key, {})['scale'] = scale_spec['default']
                 elif scale_spec is True:
                     layout.setdefault(element_key, {})['scale'] = 1.0
                 if defaults:
@@ -856,7 +856,7 @@ def defaults_from_schema(schema: Dict[str, Any]) -> Dict[str, Any]:
                         continue
                     scale_prop = (block.get('properties') or {}).get('scale')
                     if isinstance(scale_prop, dict) and 'default' in scale_prop:
-                        layout.setdefault(element_key, {})['scale'] =                             scale_prop['default']
+                        layout.setdefault(element_key, {})['scale'] = scale_prop['default']
             for element_key, block in properties.items():
                 if element_key in ('layout', 'modes') or element_key in elements:
                     continue