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/overdue/OverdueQueueState.dart

@@ -9,6 +9,7 @@ import '../../about/internal/application/NotificationType.dart';
 import '../../about/internal/application/ProofType.dart';
 import '../../about/internal/application/Standing.dart';
 import '../../about/internal/application/TextType.dart';
+import '../../designs/Checkbox.dart';
 import '../../designs/Component.dart';
 import '../../designs/Responsive.dart';
 import '../../designs/Shell.dart';
@@ -36,6 +37,9 @@ class OverdueQueueState extends State<OverdueQueue>
 
   bool _changed = false;
 
+  /// Ticked locally, awaiting the server. Rolls back on failure.
+  final Set<String> _ticked = <String>{};
+
   @override
   Widget build(BuildContext context) {
     return ViewModelBuilder<ViewOverdueQueue>.reactive(
@@ -66,6 +70,27 @@ class OverdueQueueState extends State<OverdueQueue>
     Navigator.pop(context, _changed);
   }
 
+  /// The tick completes the item outright. The Complete button still runs the
+  /// proof flow, so a task that needs an artefact has a route that asks for
+  /// one — the tick is the quick path, not the only one.
+  void _onTick(Commitment item) {
+    if (item.id == null || _ticked.contains(item.id)) {
+      return;
+    }
+
+    setState(() {
+      _ticked.add(item.id!);
+    });
+
+    _model?.complete(
+      item,
+      CompletionRequest(
+        commitmentId: item.id ?? "",
+        proofType: item.proofType.name,
+      ),
+    );
+  }
+
   void _onComplete(Commitment item) {
     // Honour proof settles immediately; everything else has to produce its
     // artefact before the completion is accepted.
@@ -526,31 +551,19 @@ class OverdueQueueState extends State<OverdueQueue>
           crossAxisAlignment: CrossAxisAlignment.start,
           mainAxisSize: MainAxisSize.min,
           children: [
-            Row(
-              crossAxisAlignment: CrossAxisAlignment.start,
-              children: [
-                Expanded(
-                  child: Column(
-                    crossAxisAlignment: CrossAxisAlignment.start,
-                    mainAxisSize: MainAxisSize.min,
-                    children: [
-                      text(item.title, 17, TextType.Medium,
-                          color: colorPrimaryDark, maxLines: 2,
-                          overflow: TextOverflow.ellipsis),
-                      const SizedBox(height: 8),
-                      text(formatWindow(item), 11, TextType.Regular,
-                          color: colorGrey2),
-                    ],
-                  ),
-                ),
-                const SizedBox(width: 10),
-                pill(
-                  classLabel(item.commitmentClass),
-                  accent,
-                  classBackground(item.commitmentClass),
-                  textSize: 9,
-                ),
-              ],
+            TickRow(
+              checked: _ticked.contains(item.id),
+              title: item.title,
+              accent: accent,
+              onTick: () => _onTick(item),
+              detail: text(formatWindow(item), 11, TextType.Regular,
+                  color: colorGrey2),
+              trailing: pill(
+                classLabel(item.commitmentClass),
+                accent,
+                classBackground(item.commitmentClass),
+                textSize: 9,
+              ),
             ),
             const SizedBox(height: 16),
             Row(
@@ -625,6 +638,7 @@ class OverdueQueueState extends State<OverdueQueue>
   @override
   void onQueueLoaded(List<Commitment> queue, Standing standing, double debt) {
     setState(() {
+      _ticked.removeWhere((id) => queue.every((item) => item.id != id));
       _queue = queue;
       _standing = standing;
       _debt = debt;