Add per-service system prompts with AI Settings tab view

Each feature service owns its system prompt in its config JSON on the
shared volume. The AI Settings page now has General and System Prompts
tabs — admins can view and edit any service's prompts at runtime with
changes taking effect within 30 s (config cache TTL).

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

features/doc-service/app/services/ai_client.py

@@ -4,7 +4,11 @@ import json
 import httpx
 
 from app.core.config import settings
-from app.services.prompts import SYSTEM_PROMPT, USER_PROMPT_TEMPLATE
+from app.services.config_reader import (
+    _DEFAULT_SYSTEM_PROMPT,
+    _DEFAULT_USER_TEMPLATE,
+    load_doc_config,
+)
 
 _client = httpx.AsyncClient(timeout=120.0)
 
@@ -19,9 +23,14 @@ async def classify_document(text: str) -> dict:
     Returns the parsed JSON result dict.
     Raises AIServiceError on HTTP errors or unexpected response shapes.
     """
+    config = await load_doc_config()
+    prompts = config.get("system_prompts", {})
+    system_prompt = prompts.get("system") or _DEFAULT_SYSTEM_PROMPT
+    user_template = prompts.get("user_template") or _DEFAULT_USER_TEMPLATE
+
     messages = [
-        {"role": "system", "content": SYSTEM_PROMPT},
-        {"role": "user", "content": USER_PROMPT_TEMPLATE.format(text=text[:50_000])},
+        {"role": "system", "content": system_prompt},
+        {"role": "user", "content": user_template.format(text=text[:50_000])},
     ]
 
     try: