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/app/services/ai_client.py

@@ -0,0 +1,49 @@
+"""HTTP client for the shared ai-service container."""
+import json
+
+import httpx
+
+from app.core.config import settings
+from app.services.prompts import SYSTEM_PROMPT, USER_PROMPT_TEMPLATE
+
+_client = httpx.AsyncClient(timeout=120.0)
+
+
+class AIServiceError(Exception):
+    pass
+
+
+async def classify_document(text: str) -> dict:
+    """
+    Send document text to ai-service for classification.
+    Returns the parsed JSON result dict.
+    Raises AIServiceError on HTTP errors or unexpected response shapes.
+    """
+    messages = [
+        {"role": "system", "content": SYSTEM_PROMPT},
+        {"role": "user", "content": USER_PROMPT_TEMPLATE.format(text=text[:50_000])},
+    ]
+
+    try:
+        response = await _client.post(
+            f"{settings.AI_SERVICE_URL}/chat",
+            json={
+                "messages": messages,
+                "max_tokens": 2048,
+                "temperature": 0,
+                "response_format": "json",
+            },
+        )
+    except httpx.RequestError as exc:
+        raise AIServiceError(f"Could not reach ai-service: {exc}") from exc
+
+    if response.status_code != 200:
+        raise AIServiceError(
+            f"ai-service returned {response.status_code}: {response.text[:200]}"
+        )
+
+    try:
+        content = response.json()["content"]
+        return json.loads(content)
+    except (KeyError, json.JSONDecodeError) as exc:
+        raise AIServiceError(f"Unexpected ai-service response: {exc}") from exc