Initial commit: CookIT recipe collection and week planner

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/planning/week_fill_test.dart

@@ -0,0 +1,65 @@
+import 'dart:math';
+
+import 'package:cookit/src/planning/week_fill.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../support/fixtures.dart';
+
+void main() {
+  final days = [for (var d = 19; d <= 25; d++) DateTime.utc(2026, 10, d)];
+  final recipes = [for (var i = 0; i < 5; i++) recipe(id: 'r$i', name: 'R$i')];
+
+  test('fills each empty day with a different Recipe, never one already in the week', () {
+    final filled = fillWeek(
+      emptyDays: days.take(3).toList(),
+      candidates: recipes,
+      inWeek: {'r0'},
+      recent: const {},
+      random: Random(1),
+    );
+    expect(filled.keys, days.take(3));
+    final ids = filled.values.map((r) => r.id).toList();
+    expect(ids.toSet(), hasLength(3));
+    expect(ids, isNot(contains('r0')));
+  });
+
+  test('recently planned Recipes come only after the others', () {
+    for (var seed = 0; seed < 20; seed++) {
+      final filled = fillWeek(
+        emptyDays: days.take(4).toList(),
+        candidates: recipes,
+        inWeek: const {},
+        recent: {'r0', 'r1'},
+        random: Random(seed),
+      );
+      final ids = filled.values.map((r) => r.id).toList();
+      expect(ids.take(3).toSet(), {'r2', 'r3', 'r4'});
+      expect(ids.last, anyOf('r0', 'r1'));
+    }
+  });
+
+  test('days stay empty when the Recipes run out', () {
+    final filled = fillWeek(
+      emptyDays: days,
+      candidates: recipes.take(2).toList(),
+      inWeek: const {},
+      recent: const {},
+      random: Random(2),
+    );
+    expect(filled, hasLength(2));
+  });
+
+  test('pickReplacement skips the week and returns null when nothing is left', () {
+    final pick = pickReplacement(
+      candidates: recipes,
+      inWeek: {'r0', 'r1', 'r2', 'r3'},
+      recent: const {},
+      random: Random(),
+    );
+    expect(pick?.id, 'r4');
+    expect(
+      pickReplacement(candidates: recipes, inWeek: {for (final r in recipes) r.id}, recent: const {}, random: Random()),
+      isNull,
+    );
+  });
+}