fix(mem0-plugin): review fixes — loop guard, v3 response format, robustness

- on_stop_cursor.sh: add loop_count guard to prevent infinite re-entry
- on_stop.sh: drop set -e so stats failure doesn't kill the reminder
- _identity.py: fix fallback stub signatures to match production (accept cwd arg)
- on_pre_compact.py: add missing infer=False on session_state writes
- on_session_start.sh: handle v3 search response format (dict with results key)
- Align all plugin versions to 0.2.1 (Claude Code, Codex, Cursor)

mem0-plugin/.codex-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "mem0",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "description": "Mem0 memory layer for AI applications. Add persistent memory, personalization, and semantic search to Codex workflows using the Mem0 Platform MCP server.",
   "author": {
     "name": "Mem0",