[Developer] #204 Phase 1 MVP — Flutter app skeleton complete

- Drift 21 tables (8 catalog + 11 user + habit_dose_variants + meta_kv)
  with R1~R10 CHECK constraints and 19 indexes
- 8 hand-crafted seed JSON catalogs in app/assets/seed/
  (refs 84, protocols 34, methodologies 21, frame_patterns 30,
   reward_menu_items 30, break_protocols 8, common_frames 5, diet_patterns 5)
- 6 domain functions: recommend_variant, compute_streak,
  validate_frame_level, active_habit_quota, weekly_minimum_ratio,
  seed_importer (transactional, idempotent)
- 4 vertical-slice Riverpod screens: HabitList, HabitCreate, CheckIn, Streak
- 31 unit tests passing; flutter analyze clean
- OQ-5 streak semantics: missing entry ≠ explicit blank
  (missing = end of history; only TrackerValue.blank triggers Never-miss-twice)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/lib/domain/recommend/recommend_variant.dart

@@ -0,0 +1,67 @@
+import '../models/habit.dart';
+
+class CheckInContext {
+  final String? location;
+  final String? condition;
+  const CheckInContext({this.location, this.condition});
+}
+
+enum RecommendReason { exactMatch, partial, fallbackMinimum, fallbackFirst }
+
+class VariantPick {
+  final HabitDoseVariantModel variant;
+  final int score;
+  final RecommendReason reason;
+  const VariantPick(this.variant, this.score, this.reason);
+}
+
+/// fn-recommend-variant: returns best variant for current context.
+/// O(N). Pure function. Returns null if habit has no variants.
+VariantPick? recommendVariant(HabitModel habit, CheckInContext ctx) {
+  final variants = habit.doseVariants;
+  if (variants.isEmpty) return null;
+
+  final scored = variants
+      .map((v) => MapEntry(v, _scoreVariant(v, ctx)))
+      .toList();
+
+  // Stable sort: score desc, then sortOrder asc.
+  scored.sort((a, b) {
+    final byScore = b.value.compareTo(a.value);
+    if (byScore != 0) return byScore;
+    return a.key.sortOrder.compareTo(b.key.sortOrder);
+  });
+
+  final best = scored.first;
+  if (best.value > 0) {
+    final reason =
+        best.value >= 4 ? RecommendReason.exactMatch : RecommendReason.partial;
+    return VariantPick(best.key, best.value, reason);
+  }
+
+  // Fallback: first is_minimum variant (by sortOrder).
+  final minimum = variants
+      .where((v) => v.isMinimum)
+      .fold<HabitDoseVariantModel?>(null,
+          (a, v) => a == null || v.sortOrder < a.sortOrder ? v : a);
+  if (minimum != null) {
+    return VariantPick(minimum, 0, RecommendReason.fallbackMinimum);
+  }
+  // No is_minimum — fall back to first by sortOrder.
+  final first = [...variants]..sort((a, b) => a.sortOrder.compareTo(b.sortOrder));
+  return VariantPick(first.first, 0, RecommendReason.fallbackFirst);
+}
+
+int _scoreVariant(HabitDoseVariantModel v, CheckInContext ctx) {
+  var s = 0;
+  if (ctx.location != null && v.contextTags.contains(ctx.location)) {
+    s += 2;
+  }
+  if (ctx.condition != null && v.conditionTags.contains(ctx.condition)) {
+    s += 2;
+  }
+  if (v.isMinimum && ctx.condition == '나쁨') {
+    s += 1;
+  }
+  return s;
+}