feat(dates): container video dates, filesystem branch, manual edit (#115)

The exiftool branch of the date waterfall now pulls raw strings with
group prefixes (one `exiftool -j -q -G1` subprocess per batch, no
`-d %s`) and classifies each candidate:

- zoned strings (own offset / Z) are true instants;
- naive strings from container groups (QuickTime/Track*/Apple) are
  UTC-rendered creation_time fields -> true instants (utc_direct).
  Running them through the camera wall-clock cascade was the
  "videos off by 4-5 hours" bug: it reinterpreted a UTC instant in
  the server zone;
- naive strings from photo-EXIF groups are camera wall clocks and run
  the offset cascade (OffsetTime* pairing + GPS evidence pulled in
  the same exiftool pass).

The legacy date_taken column stays byte-identical to the old
server-local interpretation (reproduced in Rust, DST-aware); the
new-contract date_utc / camera_offset_minutes / date_taken_tz_source
columns carry the true instant.

Manual date edit (POST /image/exif/date) reinterprets the
naive-as-UTC epoch the client sent as a wall clock in the user's
display zone (camera_tz::manual_date_resolution, tz_source =
'manual'), snapshots the pre-override new-contract triple next to the
existing legacy snapshot pair (3 new columns, migration
2026-09-25-000000), and revert restores both pairs.

ADR-0001 records the container-date finding; CLAUDE.md date-pipeline
section updated.

migrations/2026-09-25-000000_manual_date_triple_snapshot/down.sql

@@ -0,0 +1,3 @@
+ALTER TABLE image_exif DROP COLUMN original_date_utc;
+ALTER TABLE image_exif DROP COLUMN original_camera_offset_minutes;
+ALTER TABLE image_exif DROP COLUMN original_date_taken_tz_source;

migrations/2026-09-25-000000_manual_date_triple_snapshot/up.sql

@@ -0,0 +1,13 @@
+-- Manual date-edit rework (ticket #115).
+--
+-- POST /image/exif/date now writes the new-contract triple
+-- (date_utc, camera_offset_minutes, date_taken_tz_source = 'manual')
+-- alongside the legacy (date_taken, date_taken_source) pair. Reverting an
+-- override must restore the resolver's new-contract triple as well as the
+-- legacy pair, so image_exif snapshots the pre-override new-contract
+-- columns next to the existing legacy snapshot pair
+-- (original_date_taken / original_date_taken_source).
+
+ALTER TABLE image_exif ADD COLUMN original_date_utc BIGINT;
+ALTER TABLE image_exif ADD COLUMN original_camera_offset_minutes INTEGER;
+ALTER TABLE image_exif ADD COLUMN original_date_taken_tz_source TEXT;