feat(todo): filters in Todoist's language, and a view of each label (ADR 0033, D35)

A filter is a query read on the device, as the server sees no task, kept
sealed in `saved_filter`. Filters & labels is a screen of its own under
Browse; a label opens its tasks, and favourite filters and labels join
Browse's Favourites. D36 records what of Todoist's Pro stays out.

Whats-New: Filters: keep views like "today & p1", and open a label to see its tasks, under Browse in Filters & labels.
Whats-New-De: Filter: Speichere Ansichten wie „heute & p1“ und öffne ein Label, um seine Aufgaben zu sehen, in der Übersicht unter Filter & Labels.

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_server/test/integration/project/person_deletion_test.dart

@@ -53,7 +53,7 @@ void main() {
 
       test(
         'deleting a person deletes their space with every key, project, '
-        "section, task, label and settings in it, and nobody else's",
+        "section, task, label, filter and settings in it, and nobody else's",
         () async {
           for (final person in [alice, bob]) {
             await _projectOf(session, person);
@@ -106,10 +106,11 @@ const _tables = [
   'section',
   'task',
   'label',
+  'saved_filter',
   'todo_settings',
 ];
 
-/// A key, a project, a section, a task, a label and the settings in
+/// A key, a project, a section, a task, a label, a filter and the settings in
 /// [person]'s personal space, written as their device
 /// would through the sync engine (payloads stand in for sealed ones: the
 /// server never reads them).
@@ -141,6 +142,11 @@ Future<void> _projectOf(Session session, UuidValue person) =>
         Label(keyId: 'todo1.0.key', payload: sealed, nonce: sealed),
         transaction: transaction,
       );
+      await SavedFilter.db.insertRow(
+        session,
+        SavedFilter(keyId: 'todo1.0.key', payload: sealed, nonce: sealed),
+        transaction: transaction,
+      );
       await TodoSettings.db.insertRow(
         session,
         TodoSettings(keyId: 'todo1.0.key', payload: sealed, nonce: sealed),