[03-Developer] #226 Catalog Gallery 구현

- Drift schema v2: Protocols.category CHECK 6→7 (light_circadian/sleep/movement/
  nutrition/focus_cognition/recovery_stress/emotion_relationship). schemaVersion
  1→2 + onUpgrade migrateV1ToV2 (DROP+CREATE+reseed flag 클리어).
- protocols.json 34 항목 v2 재분류 (1차 효과 기준). emotion_relationship 0 매핑.
- 도메인: DisplayCategory enum (8) + CatalogItem sealed (Protocol/Break/Diet).
- 데이터: CatalogRepository.all/byId/referencesByIds (3 source 통합).
- 상태: catalog_providers.dart (catalogItems / groupedByCategory / refsByIds).
- UI: ProtocolGalleryScreen (카테고리 칩 + 카드 그리드) + ProtocolPreviewScreen
  (모든 필드 + reference 펼치기 + "내 습관으로" disabled placeholder) +
  CatalogCard / CategoryChipRow / ReferenceExpandCard. HabitListScreen 빈
  상태 CTA + AppBar 액션.
- 테스트: migration_v1_to_v2 3건 + display_category 5건 + catalog_repository
  9건 + gallery widget 3건 + preview widget 3건 = 23 신규. 기존 88 회귀 0,
  flutter analyze 0 issues. 110 passed / 1 skipped.

설계서: docs/design/226-catalog-gallery/{README, fn-catalog_repository,
fn-migration_v1_to_v2}.md + ADR-0004.

Refs #226

app/lib/domain/catalog/catalog_item.dart

@@ -0,0 +1,166 @@
+import 'display_category.dart';
+
+/// 갤러리 UI 가 소비하는 통합 카탈로그 항목.
+///
+/// 3 source (ProtocolsTable / BreakProtocolsTable / DietPatternsTable) 를
+/// 단일 sealed 계층으로 통합. 카드/필터링은 공통 필드만 보면 충분.
+sealed class CatalogItem {
+  String get id;
+  String get title;
+  String? get titleEn;
+
+  /// 카드용 1줄 요약 (≤ 60자).
+  String get summary;
+
+  DisplayCategory get displayCategory;
+
+  /// 'strong_rct' / 'meta_analysis' / 'observational' / 'mechanistic' / 'expert_opinion' / null.
+  /// DietPattern 은 'strong'/'moderate'/'mixed'/'weak'.
+  String? get evidenceStrength;
+
+  List<String> get referenceIds;
+}
+
+/// Protocols 테이블 1:1 매핑.
+final class ProtocolCatalogItem implements CatalogItem {
+  ProtocolCatalogItem({
+    required this.id,
+    required this.title,
+    required this.titleEn,
+    required this.summary,
+    required this.displayCategory,
+    required this.evidenceStrength,
+    required this.referenceIds,
+    required this.what,
+    required this.whenText,
+    required this.dose,
+    required this.why,
+    required this.how,
+    required this.checkText,
+    required this.caution,
+    required this.defaultAnchor,
+    required this.minDoseForStart,
+    required this.sourceDoc,
+  });
+
+  @override
+  final String id;
+  @override
+  final String title;
+  @override
+  final String? titleEn;
+  @override
+  final String summary;
+  @override
+  final DisplayCategory displayCategory;
+  @override
+  final String? evidenceStrength;
+  @override
+  final List<String> referenceIds;
+
+  final String what;
+  final String whenText;
+  final String dose;
+  final String why;
+  final List<String> how;
+  final String checkText;
+  final String? caution;
+  final Map<String, dynamic>? defaultAnchor;
+  final String? minDoseForStart;
+  final String? sourceDoc;
+}
+
+/// BreakProtocols 테이블 1:1 매핑. displayCategory 는 항상 breakHabit.
+final class BreakCatalogItem implements CatalogItem {
+  BreakCatalogItem({
+    required this.id,
+    required this.title,
+    required this.titleEn,
+    required this.summary,
+    required this.evidenceStrength,
+    required this.referenceIds,
+    required this.breakCategory,
+    required this.hubermanSummary,
+    required this.phases,
+    required this.defaultCommonFrames,
+    required this.tools,
+    required this.medicalWarning,
+  });
+
+  @override
+  final String id;
+  @override
+  final String title;
+  @override
+  final String? titleEn;
+  @override
+  final String summary;
+  @override
+  DisplayCategory get displayCategory => DisplayCategory.breakHabit;
+  @override
+  final String? evidenceStrength;
+  @override
+  final List<String> referenceIds;
+
+  /// 원본 break 카테고리 (alcohol / nicotine / ...). 카드 sub-tag 로 활용.
+  final String breakCategory;
+  final String hubermanSummary;
+  final List<String> phases;
+  final List<String> defaultCommonFrames;
+  final List<String> tools;
+  final String? medicalWarning;
+}
+
+/// DietPatterns 테이블 1:1 매핑. displayCategory 는 항상 nutrition.
+final class DietCatalogItem implements CatalogItem {
+  DietCatalogItem({
+    required this.id,
+    required this.title,
+    required this.titleEn,
+    required this.summary,
+    required this.evidenceStrength,
+    required this.referenceIds,
+    required this.name,
+    required this.core,
+    required this.strengths,
+    required this.weaknesses,
+    required this.koreanContextFit,
+    required this.starterLevers,
+    required this.medicalWarning,
+    required this.linkedProtocolIds,
+  });
+
+  @override
+  final String id;
+  @override
+  final String title;
+  @override
+  final String? titleEn;
+  @override
+  final String summary;
+  @override
+  DisplayCategory get displayCategory => DisplayCategory.nutrition;
+  @override
+  final String? evidenceStrength;
+  @override
+  final List<String> referenceIds;
+
+  final String name;
+  final String core;
+  final List<String> strengths;
+  final List<String> weaknesses;
+  final String? koreanContextFit;
+  final List<String> starterLevers;
+  final String? medicalWarning;
+  final List<String> linkedProtocolIds;
+}
+
+/// 그룹핑 헬퍼. 빈 카테고리 키는 결과 map 에 미포함.
+Map<DisplayCategory, List<CatalogItem>> groupByCategory(
+    List<CatalogItem> items) {
+  final result = <DisplayCategory, List<CatalogItem>>{};
+  for (final item in items) {
+    result.putIfAbsent(item.displayCategory, () => []).add(item);
+  }
+  return result;
+}