Add shared ai-service container as AI provider intermediary

All feature containers now POST messages to ai-service (port 8010) instead
of calling AI providers directly. ai-service routes to LM Studio, Ollama,
or Anthropic based on /config/ai_service_config.json. doc-service AI
providers removed; replaced by httpx ai_client.py. Backend settings
restructured to /api/settings/ai. Frontend gets dedicated AIAdminSettingsPage
and AI Service card in AppsPage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

features/doc-service/tests/conftest.py

@@ -75,12 +75,13 @@ MOCK_AI_RESULT = {
 
 
 @pytest.fixture
-def mock_ai():
-    """Patch the AI classify_document call to return MOCK_AI_RESULT."""
-    provider_mock = AsyncMock()
-    provider_mock.classify_document = AsyncMock(return_value=MOCK_AI_RESULT)
-    with patch("app.routers.documents.get_provider", return_value=provider_mock):
-        yield provider_mock
+def mock_ai_service():
+    """Patch classify_document to return MOCK_AI_RESULT without hitting ai-service."""
+    with patch(
+        "app.services.ai_client.classify_document",
+        new=AsyncMock(return_value=MOCK_AI_RESULT),
+    ) as mock:
+        yield mock
 
 
 # ── HTTP client ────────────────────────────────────────────────────────────────