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/ai-service/app/routers/health.py

@@ -0,0 +1,30 @@
+from fastapi import APIRouter
+
+from app.services.config_reader import load_ai_config
+
+router = APIRouter()
+
+
+@router.get("/health")
+async def health() -> dict:
+    return {"status": "ok"}
+
+
+@router.get("/health/provider")
+async def provider_status() -> dict:
+    config = await load_ai_config()
+    provider = config.get("provider", "lmstudio")
+    pcfg = config.get(provider, {})
+    model = pcfg.get("model", "")
+
+    # "configured" means we have the minimum required fields for the provider
+    if provider == "anthropic":
+        configured = bool(pcfg.get("api_key"))
+    else:
+        configured = bool(pcfg.get("base_url") and pcfg.get("model"))
+
+    return {
+        "provider": provider,
+        "model": model,
+        "configured": configured,
+    }