After daemon auto-export, JSONL mtime could be newer than database mtime
due to SQLite WAL mode not updating beads.db until checkpoint. This caused
validatePreExport to incorrectly block subsequent exports with "JSONL is
newer than database" error, leading to daemon shutdown.
Solution: Call TouchDatabaseFile after all export operations to ensure
database mtime >= JSONL mtime. This prevents false positives in validation
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