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/schemas/bank_account.py

@@ -0,0 +1,40 @@
+"""Bank account schemas — create, update, read, list."""
+
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class BankAccountCreate(BaseModel):
+    bank_name: str = Field(..., min_length=1, max_length=100)
+    iban: str = Field(..., min_length=1, max_length=34)
+    bic: str | None = Field(None, max_length=11)
+    account_holder: str | None = Field(None, max_length=200)
+    default_tax: str | None = Field(None, max_length=50)
+    is_default: bool = False
+
+
+class BankAccountUpdate(BaseModel):
+    bank_name: str | None = Field(None, min_length=1, max_length=100)
+    iban: str | None = Field(None, min_length=1, max_length=34)
+    bic: str | None = Field(None, max_length=11)
+    account_holder: str | None = Field(None, max_length=200)
+    default_tax: str | None = Field(None, max_length=50)
+    is_default: bool | None = None
+
+
+class BankAccountResponse(BaseModel):
+    id: str
+    bank_name: str
+    iban: str
+    bic: str | None = None
+    account_holder: str | None = None
+    default_tax: str | None = None
+    is_default: bool
+    created_at: str | None = None
+    updated_at: str | None = None
+
+
+class BankAccountListResponse(BaseModel):
+    items: list[BankAccountResponse]
+    total: int