feat(B-PLUGIN-MINIAPP-WIRE): MiniApp Registry als Singleton — gemeinsame Registry für alle Plugins

B-PLUGIN-MINIAPP-WIRE: MiniAppRegistry Singleton-Pattern
- get_miniapp_registry() / reset_miniapp_registry() in miniapp_registry.py
- Alle 6 MiniAppRegistry() Instanziierungen durch get_miniapp_registry() ersetzt
- automation/plugin.py (on_activate/on_deactivate), automation/routes.py (3x), kommunikation/plugin.py
- contracts.py: get_miniapp_registry + reset_miniapp_registry exportiert
- 0 verbleibende MiniAppRegistry() Instanziierungen außerhalb miniapp_registry.py

Tests: 12 Tests in test_miniapp_registry.py — alle grün
- Singleton, Register/List, UnregisterPlugin, Plugin-Lifecycle-Integration

app/plugins/builtins/kommunikation/miniapp_registry.py

@@ -71,3 +71,22 @@ class MiniAppRegistry:
     def get_app(self, app_id: str) -> MiniAppDef | None:
         """Get a specific mini-app definition."""
         return self._apps.get(app_id)
+
+
+# ─── Singleton helpers ───
+
+_registry: MiniAppRegistry | None = None
+
+
+def get_miniapp_registry() -> MiniAppRegistry:
+    """Return the shared singleton MiniAppRegistry instance."""
+    global _registry
+    if _registry is None:
+        _registry = MiniAppRegistry()
+    return _registry
+
+
+def reset_miniapp_registry() -> None:
+    """Reset the singleton instance (useful for tests)."""
+    global _registry
+    _registry = None