Switch read paths to the true-instant date contract (ticket #119)

- New src/date_view.rs: pure read-side functions (row_true_instant,
  row_display_wall, row_display_day, filename_true_instant) applying the
  per-source convention table for unconverted rows and the new-contract
  triple for converted rows (ADR-0001).
- /memories: grouping on the row's true instant rendered in the owner's
  display zone (prefs -> app default), not the client device offset.
  SQL is a coarse interval pre-filter over the full years-back window;
  exact month-day/week/month matching across past years happens in Rust
  (memories::day_in_span, sqlite_w_week).
- Reels: ReelSelector::Memories carries an IANA display_tz instead of a
  fixed minute offset; pre-gen params read REEL_PREGEN_DISPLAY_TZ; the
  tz_offset_minutes ledger column stores the zone offset at render time.
- Insights: prompt-facing dates render as the display wall; the
  proximity timestamp and chat context block use the true instant;
  InsightGenerator reads the owner's display zone from prefs per call.
- GpsPhotoSummary carries the new-contract triple alongside the frozen
  legacy date_taken.

Closes #119

src/state.rs

@@ -323,6 +323,7 @@ impl Default for AppState {
             face_dao.clone(),
             knowledge_dao,
             persona_dao.clone(),
+            user_ai_prefs_dao.clone(),
             libraries_vec.clone(),
         );
 
@@ -550,6 +551,7 @@ impl AppState {
             face_dao.clone(),
             knowledge_dao,
             persona_dao.clone(),
+            Arc::new(Mutex::new(Box::new(SqliteUserAiPrefsDao::new()))),
             vec![test_lib],
         );