feat(todo): rows in rounded boxes, Today as Todoist's, lists pulled to sync, a project's own colour

From the developer's review of 3 Nov 2026 (ADR 0033, D19 to D21):
- Today's tab shows today's day in its calendar, Browse the menu's lines,
  Display's button Lucide's square-menu.
- A task's row stands in a rounded box, the rows of a list a group rounded
  at its ends; the box is the row's own surface, so a chosen row's colour no
  longer shows under Upcoming's pinned week strip as the list scrolls. Its
  project and section end the line of its date at the row's right edge.
- Today has at most two groups: what is overdue, folding under its heading,
  and today's, headed "Tuesday, 3 Nov" ("Dienstag, 3. Nov."), without a
  "· Today" after it; Upcoming's days take the same form.
- Upcoming's way back to today shows whenever another day is picked.
- Today, Upcoming, the Inbox and every project pulled down sync now, an
  empty list too, as Learn's.
- A project's screen washes in its own colour, as a studyset's in Learn.
- "Add section" in place of "New section".

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/lib/l10n/app_en.arb

@@ -114,7 +114,7 @@
   "projectGone": "This project was deleted.",
   "projectMenu": "More",
   "projectPickTitle": "Project",
-  "sectionAdd": "New section",
+  "sectionAdd": "Add section",
   "sectionEdit": "Rename section",
   "sectionDelete": "Delete section",
   "sectionDeleteTitle": "Delete the section?",
@@ -778,5 +778,11 @@
         "type": "int"
       }
     }
-  }
+  },
+  "dayHeadingPattern": "EEEE, d MMM",
+  "@dayHeadingPattern": {
+    "description": "intl's DateFormat pattern of a day's heading in Today and Upcoming, as Todoist's (\"Tuesday, 3 Nov\"): EEEE the weekday, d the day, MMM the short month."
+  },
+  "overdueHide": "Hide what is overdue",
+  "overdueShow": "Show what is overdue"
 }