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>

.claude-plugin/marketplace.json

@@ -10,7 +10,7 @@
   "plugins": [
     {
       "name": "claude-mem",
-      "version": "6.0.5",
+      "version": "6.0.6",
       "source": "./plugin",
       "description": "Persistent memory system for Claude Code - context compression across sessions"
     }