chore: release v0.5.1

- Fix fallback language from ja to en
- Fix Manager context API error handling

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: recuu-pfeg

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "toban-cli",
-  "version": "0.5.0",
+  "version": "0.5.1",
   "description": "Toban Agent Runner CLI - Orchestrate AI coding agents from your terminal",
   "type": "module",
   "bin": {