Add retry_with_backoff utility (100ms base, ±25% jitter, 3 attempts)
and replace all 11 direct DAO calls in insight_chat.rs and
insight_generator.rs. The Mutex guard drops between retries so the
maintenance connection can release its SQLite write lock.
On copied or restored files (e.g. a backup library), the OS stamps
created at copy time while modified is preserved from the source, so
the earlier of the two is a better proxy for when the content
originated. Adds utils::earliest_fs_time and threads it through the
three spots that fall back to filesystem dates: photos-list sort,
memories grouping, and insight-generation timestamp.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Cameron Cordes
Cameron