feat(mem0-plugin): add PostToolUseFailure, PostCompact, SessionEnd, SubagentStop hooks

Close 4 lifecycle coverage gaps:
- PostToolUseFailure: catch failed mem0 MCP calls, classify errors, inject retry guidance
- PostCompact: inject parallel search commands for context recovery after compaction
- SessionEnd: last-chance transcript capture with dedup against Stop hook
- SubagentStop: remind parent agent to persist subagent learnings

Also patch on_stop.sh to write capture marker for SessionEnd dedup.

mem0-plugin/scripts/on_stop.sh

@@ -63,6 +63,13 @@ Always include `app_id` (the active project_id from SessionStart) as a top-level
 EOF
 
 # Capture transcript state in the background via Mem0 REST API
+SESSION_ID=$(echo "$INPUT" | jq -r '.session_id // ""' 2>/dev/null || echo "")
 echo "$INPUT" | python3 "$SCRIPT_DIR/on_pre_compact.py" --source=session-end 2>/dev/null &
 
+# Mark session as captured so SessionEnd hook can skip duplicate capture
+if [ -n "$SESSION_ID" ]; then
+  mkdir -p "$HOME/.mem0" 2>/dev/null || true
+  touch "$HOME/.mem0/.captured_${SESSION_ID}" 2>/dev/null || true
+fi
+
 exit 0