feat(todo): a project linked to a calendar shows its events beside the tasks (ADR 0033, D39)

A project's editor takes a calendar's address (https:// or webcal://,
refused otherwise), and its events show read-only, marked in the
project's colour: in Today's list and Upcoming's agenda above each day's
tasks, as blocks in the hour grids (Today's Calendar, Upcoming's 3-day)
sharing the lanes with timed tasks and all-day ones under All day, in
the project's Calendar (its agenda and month, its own events alone), and
in saved filters of days. A tap shows what an event is: when, where,
and whose calendar. The grid's lane layout is generic for it
(`layOutItems`); a task's row's box is shared (`rowBox`).

Whats-New: Link a calendar to a project in its settings: its events show beside your tasks in Today, Upcoming and the project.
Whats-New-De: Verknüpfe einen Kalender in den Einstellungen eines Projekts: Seine Termine erscheinen neben deinen Aufgaben in Heute, Demnächst und im Projekt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/test/feature/filter/filter_events_test.dart

@@ -0,0 +1,74 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_todo_flutter/src/feature/calendar/bloc/calendar_cubit.dart';
+import 'package:halkyon_todo_flutter/src/feature/calendar/model/ical.dart';
+import 'package:halkyon_todo_flutter/src/feature/filter/model/filter_events.dart';
+import 'package:halkyon_todo_flutter/src/feature/filter/model/filter_query.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/model/task.dart';
+
+/// Which events of a calendar linked to a project a saved filter shows
+/// (ADR 0033, D39): those its days take, by their project and day.
+void main() {
+  const today = Day(2026, 11, 10);
+  const world = FilterWorld(
+    today: today,
+    projects: {
+      'school': (name: 'School', parentId: null),
+      'home': (name: 'Home', parentId: null),
+    },
+  );
+
+  FeedEvent maths(Day day, {String projectId = 'school'}) => FeedEvent(
+    projectId,
+    IcalEvent(
+      uid: 'maths',
+      title: 'Maths',
+      start: DateTime(day.year, day.month, day.day, 9),
+      end: DateTime(day.year, day.month, day.day, 10),
+    ),
+  );
+
+  bool takes(String query, FeedEvent event, Day day) =>
+      switch (FilterQuery.parse(query)) {
+        FilterRead(:final query) => filterTakesEvent(query, event, day, world),
+        FilterUnread() => fail('$query not read'),
+      };
+
+  test('a filter of days takes the events on them, of its projects', () {
+    expect(takes('today', maths(today), today), isTrue);
+    expect(takes('today', maths(today.plus(1)), today.plus(1)), isFalse);
+    expect(
+      takes('7 days & #School', maths(today.plus(2)), today.plus(2)),
+      isTrue,
+    );
+    expect(
+      takes('7 days & #School', maths(today, projectId: 'home'), today),
+      isFalse,
+    );
+  });
+
+  test('a filter not of days takes none: its project, a label, no date', () {
+    expect(takes('#School', maths(today), today), isFalse);
+    expect(takes('no date', maths(today), today), isFalse);
+    expect(takes('p1 & today', maths(today), today), isFalse);
+  });
+
+  test(
+    'the events of the next four weeks a filter takes, each on its days',
+    () {
+      final events = eventsOfFilter(
+        switch (FilterQuery.parse('7 days')) {
+          FilterRead(:final query) => query,
+          FilterUnread() => fail('not read'),
+        },
+        [
+          for (var day = 0; day < 28; day++) [maths(today.plus(day))],
+        ],
+        today,
+        world,
+      );
+      expect(events.map((event) => event.$2), [
+        for (var day = 0; day < 7; day++) today.plus(day),
+      ]);
+    },
+  );
+}

apps/todo/halkyon_todo_flutter/test/feature/task/day_grid_test.dart

@@ -20,7 +20,7 @@ void main() {
     occurrence: false,
   );
 
-  String laid(List<GridBlock> blocks) => [
+  String laid(List<GridBlock<CalendarEntry>> blocks) => [
     for (final b in blocks)
       '${b.entry.task.id} ${b.start}-${b.end} ${b.lane}/${b.lanes}',
   ].join('; ');