[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/ui/screens/check_in_screen.dart

@@ -0,0 +1,82 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../core/time.dart';
+import '../../data/db/daos/tracker_dao.dart';
+import '../../state/providers.dart';
+
+class CheckInScreen extends ConsumerStatefulWidget {
+  final String habitId;
+  const CheckInScreen({super.key, required this.habitId});
+
+  @override
+  ConsumerState<CheckInScreen> createState() => _CheckInScreenState();
+}
+
+class _CheckInScreenState extends ConsumerState<CheckInScreen> {
+  bool _saving = false;
+
+  Future<void> _record(String value) async {
+    setState(() => _saving = true);
+    try {
+      final dao = ref.read(trackerDaoProvider);
+      await dao.recordCheckIn(TrackerEntryDraft(
+        habitId: widget.habitId,
+        date: _ymd(nowKst()),
+        value: value,
+      ));
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(value == 'done' ? '체크인 완료' : '오늘은 비움')),
+      );
+      Navigator.of(context).pop();
+    } catch (e) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('실패: $e')),
+      );
+    } finally {
+      if (mounted) setState(() => _saving = false);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('체크인')),
+      body: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            Text('오늘 (${_ymd(nowKst())})',
+                style: Theme.of(context).textTheme.titleLarge,
+                textAlign: TextAlign.center),
+            const SizedBox(height: 32),
+            FilledButton(
+              onPressed: _saving ? null : () => _record('done'),
+              child: const Padding(
+                padding: EdgeInsets.symmetric(vertical: 16),
+                child: Text('완료', style: TextStyle(fontSize: 18)),
+              ),
+            ),
+            const SizedBox(height: 12),
+            OutlinedButton(
+              onPressed: _saving ? null : () => _record('blank'),
+              child: const Padding(
+                padding: EdgeInsets.symmetric(vertical: 12),
+                child: Text('비움'),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+String _ymd(DateTime d) =>
+    '${d.year.toString().padLeft(4, '0')}-'
+    '${d.month.toString().padLeft(2, '0')}-'
+    '${d.day.toString().padLeft(2, '0')}';