chore: Bump version to 6.0.6

Critical bugfix for database migration issue (Issue #121)

Changes:
- Fix migration logic to always verify column existence
- Remove early return that trusted schema_versions alone
- Ensures discovery_tokens columns exist before queries
- Prevents "no such column" errors for all users

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

plugin/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "claude-mem",
-  "version": "6.0.5",
+  "version": "6.0.6",
   "description": "Persistent memory system for Claude Code - seamlessly preserve context across sessions",
   "author": {
     "name": "Alex Newman"