refactor: remove the skin system

Skins never rendered with the current scoreboard plugins: the only hook was
SportsCore._render_game in src/base_classes, which no plugin builds on, so
the UI and store already treated them as unsupported. The owner decided on
2026-09-23 to remove them outright.

Removed src/skin_system/ (runtime, base class, fixtures), skins/,
scripts/validate_skin.py and their tests; the store's "type": "skin"
installer, uninstaller and hide/refuse filters (the official registry lists
no skins); SchemaManager.inject_skin_selector; and GET /api/v3/skins.

Stored skin/skin_options config values are handled in the next commit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/blueprints/api_v3/plugins.py

@@ -1294,16 +1294,6 @@ def install_plugin():
         plugin_id = data['plugin_id']
         branch = data.get('branch')  # Optional branch parameter
 
-        # A registry skin would install but never render with the current
-        # scoreboards; refuse it with the reason rather than a generic failure
-        try:
-            registry_entry = api_v3.plugin_store_manager.get_registry_info(plugin_id)
-        except Exception:
-            registry_entry = None
-        if isinstance(registry_entry, dict) and (registry_entry.get('type') or 'plugin') == 'skin':
-            from src.skin_system import SKINS_UNSUPPORTED_MESSAGE
-            return jsonify({'status': 'error', 'message': SKINS_UNSUPPORTED_MESSAGE}), 400
-
         # Install the plugin
         # Log the plugins directory being used for debugging
         plugins_dir = api_v3.plugin_store_manager.plugins_dir
@@ -1504,13 +1494,9 @@ def get_registry_from_url():
         registry = api_v3.plugin_store_manager.fetch_registry_from_url(repo_url)
 
         if registry:
-            # Skins aren't offered: current scoreboards don't render them
             return jsonify({
                 'status': 'success',
-                'plugins': [
-                    p for p in registry.get('plugins', [])
-                    if not (isinstance(p, dict) and (p.get('type') or 'plugin') == 'skin')
-                ],
+                'plugins': registry.get('plugins', []),
                 'registry_url': repo_url
             })
         else:
@@ -1625,10 +1611,6 @@ def list_plugin_store():
         # Format plugins for the web interface
         formatted_plugins = []
         for plugin in plugins:
-            # Registry skins install but never render with the current
-            # scoreboards, so the store doesn't offer them
-            if (plugin.get('type') or 'plugin') == 'skin':
-                continue
             formatted_plugins.append({
                 'id': plugin.get('id'),
                 'name': plugin.get('name'),
@@ -2753,11 +2735,6 @@ def get_plugin_schema():
         schema = schema_mgr.load_schema(plugin_id, use_cache=True)
 
         if schema:
-            # No "Visual Skin" dropdown: the current scoreboard plugins don't
-            # render skins (src.skin_system.SKINS_UNSUPPORTED_MESSAGE), so
-            # schema_mgr.inject_skin_selector is deliberately not called. A
-            # stored "skin" value is unaffected: validation still allows it
-            # and a form save deep-merges over the stored section, keeping it.
             return jsonify({'status': 'success', 'data': {'schema': schema}})
 
         # Return a simple default schema if file not found