feat(oxibadge): warn before losing unexported review edits, add undo

The review screen now tracks whether there are edits not yet exported
and asks for confirmation before discarding them: clicking back, or
closing the app window entirely (intercepted via onCloseRequested,
which needed a core:window:allow-destroy capability that wasn't
granted by core:default). The confirmation dialog (ConfirmDialog.svelte)
is generic, built on a shared ModalFrame extracted from ExportModal so
the two don't duplicate the backdrop/box styling.

Also adds undo: a per-row button (icon-only, left of the note, shown
when that day has edits) reverts just that day instantly, and a
per-employee "undo all" (icon in a red box, last among the header's
tools) reverts every day for the current employee after a confirmation
dialog, since that one can't be undone itself.

ActionButton moves out of review/ next to IconButton/PillButton, since
ConfirmDialog (outside the review feature) now uses it too.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

oxibadge/src/lib/components/review/TimesheetTable.svelte

@@ -12,7 +12,8 @@
     oncellinput,
     onfixday,
     onaddlunch,
-    onroundday
+    onroundday,
+    onundoday
   }: {
     rows: Row[];
     rounded: Record<string, string>;
@@ -22,6 +23,7 @@
     onfixday: (di: number) => void;
     onaddlunch: (di: number) => void;
     onroundday: (di: number) => void;
+    onundoday: (di: number) => void;
   } = $props();
 </script>
 
@@ -85,6 +87,19 @@
 
           <td class="note {note.kind}">
             <span class="note-in">
+              {#if r.rowEdits > 0}
+                <button
+                  type="button"
+                  class="undo-btn"
+                  aria-label={$_('review.undo_day_aria', { values: { label } })}
+                  title={$_('review.undo_short')}
+                  onclick={() => onundoday(r.di)}
+                >
+                  <svg width="14" height="14" viewBox="0 0 24 24" aria-hidden="true" style="stroke-width: 2"
+                    ><path d="M9 14l-5-5 5-5" /><path d="M20 20v-7a4 4 0 0 0-4-4H4" /></svg
+                  >
+                </button>
+              {/if}
               {#if note.kind === 'issue'}
                 <svg width="14" height="14" viewBox="0 0 24 24" aria-hidden="true"
                   ><circle cx="12" cy="12" r="9" /><path d="M12 7.5v5.5M12 16.5h.01" /></svg
@@ -377,6 +392,33 @@
     gap: 8px;
   }
 
+  .undo-btn {
+    all: unset;
+    box-sizing: border-box;
+    width: 22px;
+    height: 22px;
+    flex: none;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border-radius: 6px;
+    color: #6e6e6e;
+    cursor: pointer;
+    transition:
+      background 0.15s,
+      color 0.15s;
+  }
+
+  .undo-btn:hover {
+    background: #262626;
+    color: #e6e6e6;
+  }
+
+  .undo-btn:focus-visible {
+    outline: 2px solid var(--ox-accent);
+    outline-offset: 1px;
+  }
+
   .empty {
     padding: 48px 24px;
     display: flex;