fix: widen undo dialog and polish its summary line

The undo/redo confirmation dialog capped at 60 columns and wrapped
even a short insert on wide terminals, showed a lowercase "snapshot
taken", a raw ISO-8601 timestamp, and lowercase yes/no labels.

Grow the dialog to fit its longest line (bounded 34–100), capitalise
Snapshot/Yes/No, and render the snapshot timestamp in local time,
human-formatted (24 May 2026, 11:00) via a new chrono dependency
(clock feature only; English month names). Yes/No capitalisation also
applies to the rebuild-confirm dialog.

docs/requirements.md

@@ -453,7 +453,11 @@ handoff-14 cleanup; 449 after B2/C2.)
   undone / re-applied (`Y` confirms). *(Implemented 2026-05-24:
   `undo` / `redo` app commands, `Modal::UndoConfirm`, runtime
   prepare→confirm→restore→refresh; `--no-undo` reports undo is off,
-  empty stacks report "nothing to undo/redo".)*
+  empty stacks report "nothing to undo/redo". UX polish 2026-05-29,
+  issue #13: the confirm dialog grows to fit its summary on one row,
+  capitalises `Snapshot` / `Yes` / `No`, and renders the snapshot
+  timestamp in local time, human-formatted (`24 May 2026, 11:00`) via
+  the new `chrono` dependency.)*
 - [x] **U3** `history.log` records every submitted command in
   append-only form, tagged with its outcome (Iteration 2;
   broadened by ADR-0034). Format: `<ISO-8601 Z>|<status>|<source>`