Add tick boxes to task rows

Tasks now carry a tick box rather than being read-only rows. Ticking strikes
the title through and leaves the item in place, so a day still reads as a
record of what was asked rather than only what is left.

New in designs/Checkbox.dart:

- TickBox   the square box itself, animating between empty and filled
- TickRow   box + struck-through title + caller-supplied detail and trailing
- addTaskAffordance  the centred "Add new task" control beneath a day's list

Applied to the home plan, the overdue queue and the goal task list. Each
screen holds a set of optimistically ticked ids so the tick lands immediately
and rolls back if the call fails; the set is reconciled whenever fresh data
arrives.

A tick completes the item outright, whatever its proof requirement. The proof
flow is still reachable from the Complete button in the overdue queue, so
tasks that need an artefact have a route that asks for one — but the tick
itself no longer enforces it.

Late completes stay visually distinct: the row keeps a Late pill and the
warning accent, and the user is told the window had already closed.

flutter analyze lib/ reports no errors.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Mfu2gQLSFN21YRBcU2NrTt

frontend/lib/Grounded/see/home/ViewHome.dart

@@ -6,6 +6,7 @@ import '../../about/external/data/pages/request/PageAndSort.dart';
 import '../../about/external/data/pages/request/Pageable.dart';
 import '../../about/external/data/pages/request/Sort.dart';
 import '../../about/external/data/pages/response/CommitmentPage.dart';
+import '../../about/external/initial/CompletionRequest.dart';
 import '../../about/external/initial/ReportCardRequest.dart';
 import '../../about/internal/application/CommitmentClass.dart';
 import '../../about/internal/application/Standing.dart';
@@ -141,6 +142,30 @@ class ViewHome extends ParentViewModel {
     }
   }
 
+  /// Ticking a row completes it. The window decides whether that lands as a
+  /// clean complete or a late one — the client never claims which.
+  void tick(Commitment item) async {
+    if (!await hasNetwork(() => tick(item))) return;
+
+    final bool late = item.wouldBeLate;
+
+    try {
+      await getDataManager().completeCommitmentEntry(CompletionRequest(
+        commitmentId: item.id ?? "",
+        proofType: item.proofType.name,
+      ));
+
+      connection.onTicked(item, late);
+
+      // Clearing an item moves the debt, so the standing has to be re-derived
+      // rather than left showing the number from before the tick.
+      loadPlan();
+    } catch (e) {
+      connection.onTickFailed(item);
+      handleError(e, () => tick(item), () => dismissError(), "Retry");
+    }
+  }
+
   /// The gate on creating anything new. Grounded blocks everything; Warned
   /// blocks electives only.
   void requestNewCommitment(Standing standing, CommitmentClass intended) async {