fix(i-d): mail-API-Brueche behoben — signatures PATCH/DELETE + labels DELETE im Backend ergaenzt, drafts PATCH->PUT

Root-Cause: Frontend-Komponenten (SignatureManager, LabelManager) rufen Endpunkte auf die das Backend nie hatte (404/405 in Production). Anders als ai/sessions sind diese Funktionen ECHT in Komponenten eingebunden -> Backend-Routen nachbestellt statt Frontend-Calls zu loeschen:

(1) PATCH+DELETE /mail/signatures/{id}: MailSignatureUpdate-Schema neu, Tenant-Scoped + Owner-Check (403 bei fremder Signatur), is_default-Exklusivitaet beim Setzen. (2) DELETE /mail/labels/{id}: gleicher Stil. (3) updateDraft Frontend: apiPatch -> apiPut (Backend hat PUT /drafts/{id} bereits). Beweistest tests/test_mail_sig_label_routes.py 5/5 gruen (PATCH-Werte, DELETE+Liste-leer, 404-Faelle).

Verifikation: create_app registriert beide neuen Routen (563 total); ruff clean; tsc exit=0.

tests/test_mail_sig_label_routes.py

@@ -0,0 +1,139 @@
+"""Tests for the mail signature PATCH/DELETE and label DELETE endpoints (I-D fix).
+
+Proves the previously missing routes now work end-to-end:
+- PATCH /api/v1/mail/signatures/{id} -> 200 with updated values
+- DELETE /api/v1/mail/signatures/{id} -> 204, row gone
+- DELETE /api/v1/mail/labels/{id} -> 204, row gone
+- 404 for unknown IDs
+"""
+
+from __future__ import annotations
+
+import pytest
+import pytest_asyncio
+from httpx import ASGITransport, AsyncClient
+from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker
+
+from app.core.db import close_engine, reset_engine_for_testing
+from app.core.permission_registry import init_permission_registry
+from app.core.service_container import get_container
+from app.main import create_app
+from app.plugins.builtins.mail import MailPlugin
+from app.plugins.registry import reset_registry_for_testing
+from app.services.plugin_service import reset_plugin_service_for_testing
+from tests.conftest import ORIGIN_HEADER, login_client, seed_tenant_and_users
+
+
+@pytest_asyncio.fixture
+async def mail_app(engine: AsyncEngine, redis_client):
+    """FastAPI app with Mail plugin registered."""
+    reset_engine_for_testing(engine)
+    app = create_app()
+    registry = reset_registry_for_testing()
+    registry.initialize(engine, app)
+    init_permission_registry(active_plugin_names={"mail"})
+    container = get_container()
+    await container.initialize()
+    registry.register_plugin(MailPlugin())
+    reset_plugin_service_for_testing(registry)
+    sf = async_sessionmaker(bind=engine, expire_on_commit=False, class_=AsyncSession)
+    async with sf() as session:
+        await registry.install(session, "mail")
+        await registry.activate(session, "mail")
+        await session.commit()
+    yield app
+    await close_engine()
+
+
+@pytest_asyncio.fixture
+async def mail_client(mail_app) -> AsyncClient:
+    transport = ASGITransport(app=mail_app)
+    async with AsyncClient(transport=transport, base_url="http://test") as c:
+        yield c
+
+
+@pytest_asyncio.fixture
+async def authed_client(
+    mail_client: AsyncClient, db_session: AsyncSession
+) -> AsyncClient:
+    seed = await seed_tenant_and_users(db_session)
+    assert seed is not None
+    await login_client(mail_client, "admin@tenanta.com")
+    return mail_client
+
+
+async def _create_signature(client: AsyncClient) -> dict:
+    resp = await client.post(
+        "/api/v1/mail/signatures",
+        json={"name": "Old Name", "body_html": "<p>old</p>", "is_default": False},
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 201, resp.text
+    return resp.json()
+
+
+async def _create_label(client: AsyncClient) -> dict:
+    resp = await client.post(
+        "/api/v1/mail/labels",
+        json={"name": "Temp Label", "color": "#ff0000"},
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 201, resp.text
+    return resp.json()
+
+
+@pytest.mark.asyncio
+async def test_update_signature(authed_client: AsyncClient):
+    sig = await _create_signature(authed_client)
+    resp = await authed_client.patch(
+        f"/api/v1/mail/signatures/{sig['id']}",
+        json={"name": "New Name", "body_html": "<p>new</p>", "is_default": True},
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 200, resp.text
+    data = resp.json()
+    assert data["name"] == "New Name"
+    assert data["body_html"] == "<p>new</p>"
+    assert data["is_default"] is True
+
+
+@pytest.mark.asyncio
+async def test_delete_signature(authed_client: AsyncClient):
+    sig = await _create_signature(authed_client)
+    resp = await authed_client.delete(
+        f"/api/v1/mail/signatures/{sig['id']}",
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 204, resp.text
+    lst = await authed_client.get("/api/v1/mail/signatures", headers=ORIGIN_HEADER)
+    assert all(s["id"] != sig["id"] for s in lst.json())
+
+
+@pytest.mark.asyncio
+async def test_delete_label(authed_client: AsyncClient):
+    label = await _create_label(authed_client)
+    resp = await authed_client.delete(
+        f"/api/v1/mail/labels/{label['id']}",
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 204, resp.text
+    lst = await authed_client.get("/api/v1/mail/labels", headers=ORIGIN_HEADER)
+    assert all(lb["id"] != label["id"] for lb in lst.json())
+
+
+@pytest.mark.asyncio
+async def test_delete_unknown_signature_404(authed_client: AsyncClient):
+    resp = await authed_client.delete(
+        "/api/v1/mail/signatures/00000000-0000-0000-0000-000000000000",
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 404, resp.text
+
+
+@pytest.mark.asyncio
+async def test_delete_unknown_label_404(authed_client: AsyncClient):
+    resp = await authed_client.delete(
+        "/api/v1/mail/labels/00000000-0000-0000-0000-000000000000",
+        headers=ORIGIN_HEADER,
+    )
+    assert resp.status_code == 404, resp.text