Add rename history with undo

- New crates/renamr-core/src/history module: HistoryBatch/HistoryEntry
  records, revert_batch() moves files back to their original paths
  (skip-on-conflict, same policy as rename::execute_renames; recreates a
  deleted destination folder defensively), push_batch() maintains a
  most-recent-first log capped at 50 batches. A partial port of the idea
  behind net.filebot.HistoryDialog, as a flat undo stack rather than a full
  session/element log. 6 new tests.
- New src-tauri/src/history.rs: persists the log as history.json in the OS
  app-config directory (same location as settings.json). execute_rename now
  takes an AppHandle and calls history::record_batch after every rename,
  recording only the items that actually got renamed. Two new commands:
  list_rename_history and undo_rename_batch.
- Frontend: the History button (previously a no-op) now opens a panel
  listing past rename batches with a timestamp, file count, and the
  old-name/new-name pairs, each with an Undo button. Undoing reconciles any
  currently-loaded item back to its pre-rename path/name, same pattern as
  post-rename reconciliation.
- Verified via cargo test (45 total)/check + npm build + a full Playwright
  pass: loaded mocked files, renamed them, opened History, undid the batch,
  and confirmed both the UI and the (mocked) backend state matched at every
  step.

src/components/RenamePanel.css

@@ -454,6 +454,57 @@
   font-size: 12.5px;
 }
 
+.history-batch-list {
+  gap: 6px;
+}
+
+.history-batch {
+  padding: 8px;
+  border-radius: 8px;
+  background: rgba(255, 255, 255, 0.02);
+}
+
+.history-batch-header {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 2px 4px 6px;
+}
+
+.history-batch-when {
+  flex: 1 1 auto;
+  min-width: 0;
+  font-size: 12px;
+  color: var(--text);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.history-batch-count {
+  flex: 0 0 auto;
+  font-size: 10.5px;
+  font-weight: 700;
+  color: var(--muted-text);
+  background: rgba(255, 255, 255, 0.05);
+  border-radius: 999px;
+  padding: 2px 8px;
+}
+
+.history-undo-button {
+  flex: 0 0 auto;
+  width: auto;
+  height: 26px;
+  padding: 0 12px;
+  font-size: 11.5px;
+}
+
+.history-batch-entries {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
 .status-bar {
   position: absolute;
   left: 18px;