fix: v0.2.8 — init cooldown to prevent repeated failed-login hammering

Cache failed `_ensure_initialized` outcomes for 60 seconds so that
repeated tool calls during a credential outage (wrong password,
IP-blocked 407, DNS failure) don't keep hammering DSM. Each caller
gets the same exception raised from the cache until the cooldown
window expires, after which a fresh attempt is made.

- Adds INIT_ERROR_COOLDOWN module constant (60.0 s).
- Adds self._init_error / self._init_error_until state on DsmClient.
- Re-raises cached error inside the init lock, emits warning log on
  cache entry.

Addresses M4 from the 0.2.7 review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

uv.lock

@@ -362,7 +362,7 @@ wheels = [
 
 [[package]]
 name = "mcp-synology-container"
-version = "0.2.7"
+version = "0.2.8"
 source = { editable = "." }
 dependencies = [
     { name = "click" },