feat: Mini-Apps registry, Stammdaten backend persistence, bank accounts

- Register 6 mini-apps in kommunikation plugin (contact_picker, file_share,
  calendar_invite, mail_forward, ai_search, task_create)
- Connect AdressenTab to backend API (GET/POST/PATCH/DELETE /addresses)
- Create BankAccount model, schema, service, routes + migration 0033
- Connect KontenTab to backend API (GET/POST/PATCH/DELETE /bank-accounts)
- AI tools already working: 7 tools registered (hybrid_search, get_contact_mails, etc.)

app/plugins/builtins/kommunikation/plugin.py

@@ -71,7 +71,57 @@ class KommunikationPlugin(BasePlugin):
         miniapp_registry = MiniAppRegistry()
         service_container.register("comm_miniapps", miniapp_registry)
 
-        logger.info("Kommunikation plugin activated — WebSocket + MiniApp registries ready")
+        # Register built-in mini-apps
+        miniapp_registry.register(
+            app_id="contact_picker",
+            name="Kontakt wählen",
+            icon="👤",
+            description="Kontakt aus dem CRM im Chat teilen",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"contact_id": {"type": "string"}}},
+        )
+        miniapp_registry.register(
+            app_id="file_share",
+            name="Datei teilen",
+            icon="📎",
+            description="Datei aus dem DMS im Chat teilen",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"file_id": {"type": "string"}}},
+        )
+        miniapp_registry.register(
+            app_id="calendar_invite",
+            name="Termin teilen",
+            icon="📅",
+            description="Kalender-Termin im Chat teilen",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"event_id": {"type": "string"}}},
+        )
+        miniapp_registry.register(
+            app_id="mail_forward",
+            name="E-Mail weiterleiten",
+            icon="✉️",
+            description="E-Mail im Chat weiterleiten",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"mail_id": {"type": "string"}}},
+        )
+        miniapp_registry.register(
+            app_id="ai_search",
+            name="KI Suche",
+            icon="🔍",
+            description="KI-gestützte Suche im CRM starten",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"query": {"type": "string"}}},
+        )
+        miniapp_registry.register(
+            app_id="task_create",
+            name="Aufgabe erstellen",
+            icon="✅",
+            description="Aufgabe aus dem Chat erstellen",
+            plugin_name="kommunikation",
+            render_schema={"type": "object", "properties": {"title": {"type": "string"}, "due_date": {"type": "string"}}},
+        )
+
+        logger.info("Kommunikation plugin activated — WebSocket + MiniApp registries ready (6 mini-apps registered)")
 
     async def on_deactivate(self, db, service_container, event_bus) -> None:
         """Clean up registries."""