feat: add 5 notification mutations + comprehensive refactors from PR review

New notification actions (archive_many, create_unique, unarchive_many,
unarchive_all, recalculate) bring unraid_notifications to 14 actions.

Also includes continuation of CodeRabbit/PR review fixes:
- Remove redundant try-except in virtualization.py (silent failure fix)
- Add QueryCache protocol with get/put/invalidate_all to core/client.py
- Refactor subscriptions (manager, diagnostics, resources, utils)
- Update config (logging, settings) for improved structure
- Expand test coverage: http_layer, safety guards, schema validation
- Minor cleanups: array, docker, health, keys tools

Co-authored-by: Claude <noreply@anthropic.com>

unraid_mcp/subscriptions/resources.py

@@ -4,8 +4,10 @@ This module defines MCP resources that bridge between the subscription manager
 and the MCP protocol, providing fallback queries when subscription data is unavailable.
 """
 
+import asyncio
 import json
 import os
+from typing import Final
 
 import anyio
 from fastmcp import FastMCP
@@ -16,22 +18,29 @@ from .manager import subscription_manager
 
 # Global flag to track subscription startup
 _subscriptions_started = False
+_startup_lock: Final[asyncio.Lock] = asyncio.Lock()
 
 
 async def ensure_subscriptions_started() -> None:
     """Ensure subscriptions are started, called from async context."""
     global _subscriptions_started
 
+    # Fast-path: skip lock if already started
     if _subscriptions_started:
         return
 
-    logger.info("[STARTUP] First async operation detected, starting subscriptions...")
-    try:
-        await autostart_subscriptions()
-        _subscriptions_started = True
-        logger.info("[STARTUP] Subscriptions started successfully")
-    except Exception as e:
-        logger.error(f"[STARTUP] Failed to start subscriptions: {e}", exc_info=True)
+    # Slow-path: acquire lock for initialization (double-checked locking)
+    async with _startup_lock:
+        if _subscriptions_started:
+            return
+
+        logger.info("[STARTUP] First async operation detected, starting subscriptions...")
+        try:
+            await autostart_subscriptions()
+            _subscriptions_started = True
+            logger.info("[STARTUP] Subscriptions started successfully")
+        except Exception as e:
+            logger.error(f"[STARTUP] Failed to start subscriptions: {e}", exc_info=True)
 
 
 async def autostart_subscriptions() -> None: