feat(todo): a project's Calendar, Upcoming's Display and its 3-day grid (ADR 0033, D17)

A project's Display gains the Calendar layout: Upcoming's week strip
and agenda, now shared as DayAgenda, over the project's tasks it keeps,
with No date beside the month and Future occurrences, each repeating
task also on the days it will come back (calendarOf on Repeat.next),
muted, neither ticked off nor dragged.

Upcoming gets a Display of its own, the same sheet over another target
(DisplayTarget): Agenda or 3-day, done tasks, future occurrences,
sorting, the filters by deadline, priority and label, and in the grid
Colouring by priority, label or project. It is kept in the person's
settings, one sealed row under an ID keyed by the account in the new
synced table todo_settings (migration settings: the table, its index
on spaceId and its foreign key to the space, cascading on delete).

The 3-day grid shows today and the two days after, stepped or swiped
three at a time: tasks without a time all day, timed ones as blocks as
long as they last, overlapping ones side by side (layOutDay). A long
press on a half hour adds a task there for half an hour; Overdue opens
the overdue tasks with Reschedule.

The board's separator builder names its BuildContext, as the root's
analyzer plugin asks (never_discard_build_context).

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_client/lib/migrations/migration_registry.dart

@@ -6,6 +6,7 @@ import 'package:serverpod_database/serverpod_database.dart';
 
 part '20261101000019144-projects/migration.dart';
 part '20261101000604776-tasks/migration.dart';
+part '20261101180755366-settings/migration.dart';
 
 /// Migration registry for the client-side database.
 class MigrationRegistry {
@@ -14,6 +15,7 @@ class MigrationRegistry {
   static final List<MigrationVersionSql> migrations = [
     _Migration20261101000019144_projects(),
     _Migration20261101000604776_tasks(),
+    _Migration20261101180755366_settings(),
   ];
 
   /// List of all client-side database migration versions.