Migration 015 did a one-time rebuild of recipes_fts at creation time but
omitted triggers, so rows inserted after that point were invisible to MATCH
queries. Adds AFTER INSERT/UPDATE/DELETE triggers to 015 (fresh DBs / tests)
and migration 016 to backfill them on existing databases.
Fixes 3 failing tests: test_search_recipes_by_ingredient_names,
test_level1_returns_ranked_suggestions, test_level2_returns_swap_candidates.