[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/ui/widgets/catalog_card.dart

@@ -0,0 +1,105 @@
+import 'package:flutter/material.dart';
+
+import '../../domain/catalog/catalog_item.dart';
+
+class CatalogCard extends StatelessWidget {
+  const CatalogCard({super.key, required this.item, required this.onTap});
+
+  final CatalogItem item;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    final dc = item.displayCategory;
+    return Semantics(
+      label: '${dc.label} 카테고리. ${item.title}. ${item.summary}',
+      button: true,
+      child: Card(
+        clipBehavior: Clip.antiAlias,
+        child: InkWell(
+          onTap: onTap,
+          child: Padding(
+            padding: const EdgeInsets.all(12),
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Row(
+                  children: [
+                    Icon(dc.icon, size: 18),
+                    const SizedBox(width: 6),
+                    Expanded(
+                      child: Text(
+                        item.title,
+                        style: Theme.of(context).textTheme.titleMedium,
+                        maxLines: 1,
+                        overflow: TextOverflow.ellipsis,
+                      ),
+                    ),
+                  ],
+                ),
+                if (item.titleEn != null) ...[
+                  const SizedBox(height: 2),
+                  Text(
+                    item.titleEn!,
+                    style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                          color: Colors.grey,
+                        ),
+                    maxLines: 1,
+                    overflow: TextOverflow.ellipsis,
+                  ),
+                ],
+                const SizedBox(height: 8),
+                Expanded(
+                  child: Text(
+                    item.summary,
+                    style: Theme.of(context).textTheme.bodySmall,
+                    maxLines: 3,
+                    overflow: TextOverflow.ellipsis,
+                  ),
+                ),
+                if (item.evidenceStrength != null) ...[
+                  const SizedBox(height: 6),
+                  _EvidenceBadge(strength: item.evidenceStrength!),
+                ],
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+class _EvidenceBadge extends StatelessWidget {
+  const _EvidenceBadge({required this.strength});
+
+  final String strength;
+
+  @override
+  Widget build(BuildContext context) {
+    final (label, color) = switch (strength) {
+      'strong_rct' || 'strong' => ('근거 강함', Colors.green),
+      'meta_analysis' => ('메타분석', Colors.teal),
+      'moderate' => ('근거 중간', Colors.blue),
+      'observational' => ('관찰연구', Colors.blueGrey),
+      'mechanistic' => ('기전', Colors.orange),
+      'expert_opinion' => ('전문가 의견', Colors.brown),
+      'mixed' => ('근거 혼재', Colors.amber),
+      'weak' => ('근거 약함', Colors.grey),
+      _ => (strength, Colors.grey),
+    };
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 2),
+      decoration: BoxDecoration(
+        color: color.withValues(alpha: 0.15),
+        border: Border.all(color: color),
+        borderRadius: BorderRadius.circular(4),
+      ),
+      child: Text(
+        label,
+        style: TextStyle(fontSize: 11, color: color),
+      ),
+    );
+  }
+}