refactor: simplify path validation and connection_init via shared helpers

- Extract _validate_path() in unraid.py — consolidates traversal check + normpath
  + prefix validation used by disk/logs and live/log_tail into one place
- Extract build_connection_init() in subscriptions/utils.py — removes 4 duplicate
  connection_init payload blocks from snapshot.py (×2), manager.py, diagnostics.py;
  also fixes diagnostics.py bug where x-api-key: None was sent when no key configured
- Remove _LIVE_ALLOWED_LOG_PREFIXES alias — direct reference to _ALLOWED_LOG_PREFIXES
- Move import hmac to module level in server.py (was inside verify_token hot path)

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

uv.lock

@@ -1572,7 +1572,7 @@ wheels = [
 
 [[package]]
 name = "unraid-mcp"
-version = "1.1.1"
+version = "1.1.2"
 source = { editable = "." }
 dependencies = [
     { name = "fastapi" },