Include custom meals in Product/Food search results

[LarytheLord]

Summary

Custom meals were only discoverable in the Recently added tab, because Product/Food search paths queried remote OFF/FDC sources only. This made reusing manually created meals hard, as reported in #267.

This PR includes matching custom meals from recent intake at the top of both Product and Food search results.

Changes

• Extend SearchProductsUseCase to read recent intake via GetIntakeUsecase.
• For non-empty search strings:
  • filter recent meals to MealSourceEntity.custom
  • match on name/brand case-insensitively
  • prepend matches before remote OFF/FDC results
  • deduplicate by source + code/name
• Update DI wiring in locator.dart for the new use case dependency.
• Add search_products_usecase_test.dart covering:
  • custom meal inclusion in OFF search
  • deduplication behavior
  • no local lookup for blank queries

Notes

I could not execute Flutter tests in this environment because flutter is not installed (command not found).

[LarytheLord]

Pushed a follow-up technical pass in commit 40c5232 to strengthen coverage for this search behavior:\n\n- added a test that verifies custom meals can match by brand (case-insensitive), not only by name\n- added a test that verifies deduplication still works when custom meals have no code (fallback name-based key path)\n\nThis should make the custom-meal prepend logic safer against edge cases in real intake history.