feat(todo): a project's editor as Todoist's Add project, with sub-projects and favourites

Adding or editing a project was a dialog of a name and a colour. It is
now a screen of its own on a phone (a dialog where sheets are dialogs),
as Todoist's Add project: the name counted to 120, a description, the
colour, the parent project, a Favourite switch and the layout, Display's
pictures. All of it lives in the project's sealed payload, the schema
still 1, no server model or migration; the payload now keeps fields it
doesn't know, as a task's does.

A new project starts with the layout picked, and Display's Reset all
returns to that default rather than to List. Browse lists sub-projects
indented and folding under their parents, and the favourites in a group
above; a project is never offered as its own ancestor, and a parent's
deletion takes its sub-projects, naming them first, as Todoist's. ADR
0033, D28.

Whats-New: Add project and Edit project are a screen of their own, with a description, a parent project, Favourite and the layout.
Whats-New: Browse lists sub-projects under their parents and your favourite projects at the top.
Whats-New: Reset all in Display returns to the layout the project was made with.
Whats-New-De: „Projekt hinzufügen“ und „Projekt bearbeiten“ sind eine eigene Seite, mit Beschreibung, übergeordnetem Projekt, Favorit und Layout.
Whats-New-De: „Übersicht“ zeigt Unterprojekte unter ihren Projekten und deine Favoriten oben.
Whats-New-De: „Alles zurücksetzen“ in der Anzeige kehrt zum Layout zurück, mit dem das Projekt angelegt wurde.

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

docs/adr/0033-halkyon-todo.md

@@ -461,6 +461,32 @@ The developer's review of 4 Nov 2026, again beside Todoist's screens.
 - **D27 Listed in F-Droid as *Task* and *Calendar & Agenda*** (the developer's, both,
   over *Time*, which F-Droid's categories give to clocks and timers): no other app of
   the repository used *Time*, so the repository no longer lists it.
+- **D28 A project's editor as Todoist's Add project, with sub-projects and
+  favourites** (the developer's, over the dialog of a name and a colour): a screen of its
+  own on a phone (*Add project*, *Edit project*, ← and ✓ in its app bar), the same in a
+  dialog where sheets are dialogs; the name counted to 120, a description, then rounded
+  rows: the colour (its palette name, opening the picker), the parent project (*No
+  parent* or a project, from a sheet listing them indented; never the project itself
+  nor any project below it, `parentChoices`, so none becomes its own ancestor), a
+  Favourite switch; then the Layout, Display's pictures (`LayoutPicker`). All of it is
+  **in the project's sealed payload** (`description`, `parentId`, `favorite`,
+  `defaultView`), no server model changed, no migration, the schema still 1; the payload
+  now keeps the fields it doesn't know, as a task's (D18), so a later version's survive
+  an edit here (a 0.2.0 device editing a project still drops these). **The default
+  Display**: a new project starts with the layout picked, and Display's *Reset all*
+  returns to it (`defaultView`, the dot on Display marking a Display that differs from
+  it); the editor sets its layout, and a layout picked anew there shows at once.
+  Projects made before keep List as their default. **Browse** lists each project's
+  sub-projects indented under it, folding under its chevron (the fold not kept, agent's
+  choice: a choice of the device, and quick to make again), and the favourite projects
+  in a *Favourites* group above the projects. A project whose parent is gone or doesn't
+  open here, or projects whose parents run in a circle (two devices each moving one
+  under the other), stand as projects of their own, none lost (`projectTree`). **Deleting
+  a project deletes its sub-projects**, with their sections and tasks, as Todoist does,
+  the confirmation naming them first (`TodoPerson.deleteProject`). *Alternatives:* the
+  sub-projects moved up a level (kept, but surprising after a confirmation that named
+  only the parent); a depth limit as Todoist's (four levels), left until deep trees turn
+  out to be a problem.
 
 ## Steps