Populate the new-contract date columns at ingest while keeping the
legacy date_taken column byte-identical (ADR-0001):
- camera_tz module: offset cascade (offset tag -> GPS zone -> server
zone) as a pure, testable function; bundled offline TZF geometry for
GPS -> IANA resolution; DST-correct offsets for the capture date;
display-zone helpers (DEFAULT_DISPLAY_TZ, display_zone_for,
display_zone_offset_minutes) for the read-side cutover.
- EXIF branch: kamadak-exif now collects OffsetTime* tags paired with
the winning date tag; resolve_date_taken takes an ExifPrior and
emits (date_utc, camera_offset_minutes, date_taken_tz_source) per
branch: exif -> cascade, exiftool/fs_time -> utc_direct, filename
-> unclassified (pending #116).
- Schema: migration adds image_exif.date_utc /
camera_offset_minutes / date_taken_tz_source and
user_ai_prefs.display_tz (all nullable; down.sql drops them).
- DAO + ingest: backfill_date_taken persists the triple alongside the
legacy pair; watcher, upload, and set_image_gps call sites feed the
cascade.
- Response surface: ExifMetadata and ExifSummary carry the triple so
/image/metadata and /photos/exif expose it (null for unconverted
rows); reel requests mirror display_tz into prefs.
cargo build + clippy clean; 625 lib + 702 bin tests pass (the one
failing doctest in utils.rs is pre-existing at the base commit).
