feat(todo): comments and descriptions in the editor (ADR 0033, D38)

Comments and the descriptions of tasks, projects, sections and filters
become the editor's document on halkyon_editor; names and titles stay
text. Rows written as text read as notes and become documents when next
saved, the server seeing only sealed bytes, so there is no migration.

Sections' descriptions can now be written, and a project's shows above
its tasks. Android answers whether a link can open only for what is
declared, so Todo declares http and https.

Whats-New: Comments and descriptions take rich text: headings, lists, checklists, links and more.
Whats-New-De: Kommentare und Beschreibungen können jetzt formatiert werden: Überschriften, Listen, Checklisten, Links und mehr.

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/pubspec.yaml

@@ -41,6 +41,9 @@ dependencies:
   # Primitives every Halkyon package shares: `CoalescingRunner`.
   halkyon_core:
     path: ../../../packages/halkyon_core
+  # Comments and descriptions as rich text (ADR 0033, D38).
+  halkyon_editor:
+    path: ../../../packages/halkyon_editor
   halkyon_oidc_flutter:
     path: ../../../packages/halkyon_oidc_flutter
   halkyon_todo_client: