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/providers/__init__.py

@@ -0,0 +1,20 @@
+from app.providers.base import AIProvider
+
+
+def get_provider(ai_config: dict) -> AIProvider:
+    """Return an AIProvider instance for the active provider in the config."""
+    provider_name = ai_config.get("provider", "lmstudio")
+    provider_cfg = ai_config.get(provider_name, {})
+
+    match provider_name:
+        case "anthropic":
+            from app.providers.anthropic_provider import AnthropicProvider
+            return AnthropicProvider(provider_cfg)
+        case "ollama" | "lmstudio":
+            from app.providers.openai_compat import OpenAICompatProvider
+            return OpenAICompatProvider(provider_cfg, provider_name=provider_name)
+        case _:
+            raise ValueError(f"Unknown AI provider: {provider_name!r}")
+
+
+__all__ = ["AIProvider", "get_provider"]