feat(add-meal): suggest a meal type from the current time (#580)

[ibrahim-iqbal]

Fixes #580.

Summary

Preselect a meal type in the global add-item bottom sheet based on the device's local time. Every tile stays immediately tappable; the suggestion renders as a small Suggested chip on the matching tile so nothing changes about the tap flow.

Approach

• New MealTypeSuggester.suggestFromTime(DateTime) in lib/core/utils/ centralizes the time-of-day ranges so they can be tweaked in one place:
  • Breakfast: 04:00 – 10:59
  • Lunch: 11:00 – 14:59
  • Snack: 15:00 – 16:59
  • Dinner: 17:00 – 21:59
  • Snack: 22:00 – 03:59 (late night / pre-dawn)
• AddItemBottomSheet accepts a nullable suggestedType. The global + action in main_screen.dart passes MealTypeSuggester.suggestFromTime(DateTime.now()). Flows launched from a specific meal section keep passing nothing and see no highlight, per the acceptance criteria.
• The Suggested chip uses colorScheme.secondaryContainer / onSecondaryContainer so it inherits both light and dark themes cleanly.

Acceptance criteria mapping

• Define time ranges in one testable helper — MealTypeSuggester
• Use device local time to determine the initial suggestion — MealTypeSuggester.suggestFromTime(DateTime.now()) in main_screen.dart
• Visually preselect the suggested meal type when opened from global + — Suggested chip on the matching tile
• Let the user choose a different meal type before continuing — every tile stays tappable (unchanged onTap handlers)
• Do not change flows launched from a specific meal section — those callers keep passing nothing, so suggestedType stays null and no chip renders
• Handle boundary times deterministically — inclusive-start / exclusive-end ranges; boundary hours (04, 11, 15, 17, 22, 00, 03:59) covered in tests
• Add unit / widget tests covering each range, boundaries, and explicit meal-section behavior — 6 unit tests + 2 widget tests
• Add or preserve stable Semantics(identifier: ...) values — chip has add-item-suggested-chip; the existing tile identifiers are untouched

Tests

• test/core/utils/meal_type_suggester_test.dart — 6 unit tests covering every range and each boundary hour
• test/core/presentation/widgets/add_item_bottom_sheet_test.dart — 2 new widget tests: chip renders on the matching tile, no chip renders when suggestedType is null

All 11 tests in the two files pass; flutter analyze clean on the touched files.

Localization

Adds suggestedLabel: "Suggested" to lib/l10n/intl_en.arb. Other locales fall back to English until they're translated.