fix(mem0-plugin): sanitize marker path, add pre-compact REST backup, fix cross-tool gaps

- Sanitize project_id in onboard marker path (tr '/:' '--') to handle
  slashes from env var overrides
- Fire on_pre_compact.py REST backup from PreCompact hook (was only
  called from Stop hooks — crash before Stop = data loss)
- Source _identity.sh in on_stop_codex.sh and on_stop_cursor.sh so
  MEM0_PROJECT_ID + API key fallback are available
- Note dream --schedule is Claude Code-only (Codex/Cursor lack schedule)

mem0-plugin/scripts/on_pre_compact.sh

@@ -15,6 +15,13 @@ if [ -n "${MEM0_DEBUG:-}" ]; then
   mkdir -p "$HOME/.mem0" && exec 2>>"$HOME/.mem0/hooks.log"
 fi
 
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+INPUT=$(cat)
+
+# Fire REST API transcript backup in background (safety net if agent
+# can't complete the add_memory call before compaction finishes)
+echo "$INPUT" | python3 "$SCRIPT_DIR/on_pre_compact.py" --source=pre-compaction 2>/dev/null &
+
 cat <<'EOF'
 ## CRITICAL: Pre-Compaction Session Summary