[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/streak/weekly_minimum_ratio.dart

@@ -0,0 +1,66 @@
+import '../models/habit.dart';
+import '../models/tracker_entry.dart';
+
+/// fn-weekly-minimum-ratio
+///
+/// Computes the share of done check-ins in the last 7 days that used the
+/// habit's "minimum" dose variant. Useful for L2-conditional habits where the
+/// user picks a minimum option on bad-condition days. A high ratio is fine
+/// (the protocol's whole point), but it also signals the user is mostly
+/// running on minimum dose — a context the UI can surface.
+///
+/// Returns 0.0 when there are no done entries in the window (no division by
+/// zero).
+class WeeklyMinimumRatio {
+  final int totalDone;
+  final int minimumUsed;
+  final double ratio; // 0.0..1.0
+  final DateTime windowStart; // inclusive, YYYY-MM-DD == windowStart
+  final DateTime windowEnd; // inclusive
+
+  const WeeklyMinimumRatio({
+    required this.totalDone,
+    required this.minimumUsed,
+    required this.ratio,
+    required this.windowStart,
+    required this.windowEnd,
+  });
+}
+
+/// Pure function: caller resolves the variant rows and passes them in.
+///
+/// - [entries] should already be filtered to the habit and to value=done.
+/// - [variantsById] maps variant_id → variant (only minimums need to be
+///   present, but a full map is fine).
+/// - [asOf] is treated as the inclusive end of the 7-day window.
+WeeklyMinimumRatio computeWeeklyMinimumRatio({
+  required Iterable<TrackerEntryModel> entries,
+  required Map<String, HabitDoseVariantModel> variantsById,
+  required DateTime asOf,
+}) {
+  final end = DateTime(asOf.year, asOf.month, asOf.day);
+  final start = end.subtract(const Duration(days: 6));
+
+  var totalDone = 0;
+  var minimumUsed = 0;
+
+  for (final e in entries) {
+    if (e.value != TrackerValue.done) continue;
+    final d = DateTime.parse(e.date);
+    if (d.isBefore(start) || d.isAfter(end)) continue;
+    totalDone += 1;
+    final vId = e.variantId;
+    if (vId == null) continue;
+    final v = variantsById[vId];
+    if (v != null && v.isMinimum) minimumUsed += 1;
+  }
+
+  final ratio = totalDone == 0 ? 0.0 : minimumUsed / totalDone;
+  return WeeklyMinimumRatio(
+    totalDone: totalDone,
+    minimumUsed: minimumUsed,
+    ratio: ratio,
+    windowStart: start,
+    windowEnd: end,
+  );
+}