[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/rules/xor_protocol.dart

@@ -0,0 +1,20 @@
+import '../models/habit.dart';
+
+/// XOR: build → protocol_id (only); break → break_protocol_id (only).
+void assertXorProtocol({
+  required HabitType type,
+  required String? protocolId,
+  required String? breakProtocolId,
+}) {
+  if (type == HabitType.build) {
+    if (protocolId == null || breakProtocolId != null) {
+      throw ArgumentError(
+          'build habit requires protocol_id and no break_protocol_id');
+    }
+  } else {
+    if (breakProtocolId == null || protocolId != null) {
+      throw ArgumentError(
+          'break habit requires break_protocol_id and no protocol_id');
+    }
+  }
+}