Nullable TEXT column stores JSON section config. Null means use defaults.
No data backfill needed for existing divers.

New field with copyWith support and clear-to-defaults flag.
SettingsNotifier gets set and reset methods for the section config.

JSON serialization via DiveDetailSectionConfig.sectionsFromJson/toJson.
Stores null when config matches defaults to avoid unnecessary writes.

ReorderableListView with visibility toggle switches per section.
Reset to Default in overflow menu. Dimmed styling for hidden sections.

Navigation tile in Appearance links to /settings/dive-detail-sections.
New GoRoute wires the DiveDetailSectionsPage into the router.

Replace hardcoded section order with a registry map and loop over the
user's diveDetailSections config. Fixed sections (header, profile)
remain at the top. All data-driven auto-hide conditions preserved.

The previous code used List == (reference equality) to detect defaults
and write null. This always evaluates to false for loaded lists,
breaking the reset-to-defaults flow. Simplify by always writing JSON.

The settings page uses a separate _AppearanceSectionContent widget
for the master-detail layout on desktop. The new section was only
added to the mobile AppearancePage, not the desktop inline version.

Add 17 new tests (32 -> 49 total) covering:
- Model: fromJson missing visible field, fromJson unknown ID throws,
  copyWith no-args, round-trip serialization, ensureAllSections with
  empty list and custom visibility preservation
- Widget: toggle switch updates visibility, hidden section has reduced
  opacity, reset-to-default menu, initial switch state, app bar title,
  section descriptions
- AppSettings: copyWith preserves when unset, defaults match static
  const, clearDiveDetailSections takes precedence

Add 20 more tests (49 -> 69 total) covering:
- Model: fromJson explicit false, single-item round-trip, tryFromJson
  success/missing-id/non-string-id, sectionsFromJson with map-JSON/
  non-map-list-items/all-unknown-IDs/mixed-types, ensureAllSections
  preserves custom visibility, every displayName/description value,
  unique displayName constraint
- Widget: toggle back on restores opacity, multiple independent
  toggles, overflow menu present, subheading text, custom initial
  section order via provider override
- AppSettings: sequential copyWith independence, empty list, custom
  constructor

Add widget tests for dataSources, buddies, sightings, signatures, details, and all-sections-together rendering. Extract _buildTestWidget
extraOverrides parameter and _alwaysRenderOverrides helper for sections that require additional provider stubs.

PR #95 (duration->bottomTime rename) claimed migration v56. Bump the
dive_detail_sections column addition to v57 and update schemaVersion.

- Bump migration from v56 to v57 (PR #95 claimed v56 for the
  duration->bottom_time column rename)
- Regenerate Drift code against updated schema
- Add missing setDiveDetailSections/resetDiveDetailSections stubs
  to MockSettingsNotifier