feat(notifications): add overlay notifications with position config

- Add Catppuccin Macchiato overlay notification stack with 3s transient timeout
- Add `notifications.overlayPosition` config (top-left | top | top-right)
- Route startup tokenization and subtitle annotation status through configured surfaces
- Deduplicate rapid subtitle mode toggle notifications
- Change `both` to mean overlay + system; add `osd-system` as legacy alias for old behavior
- Keep `osd`/`osd-system` as config-file-only legacy values; Settings UI offers overlay/system/both/none

src/renderer/overlay-notifications.test.ts

@@ -0,0 +1,65 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import {
+  createOverlayNotificationStore,
+  handleOverlayNotificationEvent,
+  overlayNotificationPositionClass,
+} from './overlay-notifications';
+
+test('overlay notification store caps transient notifications and keeps pinned jobs visible', () => {
+  const store = createOverlayNotificationStore({ maxVisible: 3 });
+
+  store.upsert({
+    id: 'character-dictionary-auto-sync',
+    title: 'Character dictionary',
+    body: 'Generating character dictionary',
+    persistent: true,
+  });
+  store.upsert({ id: 'one', title: 'One', body: 'First' });
+  store.upsert({ id: 'two', title: 'Two', body: 'Second' });
+  store.upsert({ id: 'three', title: 'Three', body: 'Third' });
+
+  assert.deepEqual(
+    store.visible().map((entry) => entry.id),
+    ['character-dictionary-auto-sync', 'two', 'three'],
+  );
+
+  store.upsert({
+    id: 'character-dictionary-auto-sync',
+    title: 'Character dictionary',
+    body: 'Ready',
+    persistent: false,
+  });
+
+  assert.deepEqual(
+    store.visible().map((entry) => `${entry.id}:${entry.body}`),
+    ['two:Second', 'three:Third', 'character-dictionary-auto-sync:Ready'],
+  );
+});
+
+test('overlay notification positions map to stack alignment classes', () => {
+  assert.equal(overlayNotificationPositionClass(undefined), 'position-top-right');
+  assert.equal(overlayNotificationPositionClass('top-left'), 'position-top-left');
+  assert.equal(overlayNotificationPositionClass('top'), 'position-top');
+  assert.equal(overlayNotificationPositionClass('top-right'), 'position-top-right');
+});
+
+test('overlay notification event handler dismisses notifications by id', () => {
+  const calls: string[] = [];
+
+  handleOverlayNotificationEvent(
+    {
+      show: (payload) => {
+        calls.push(`show:${payload.id ?? ''}:${payload.title}`);
+        return payload.id ?? '';
+      },
+      remove: (id) => {
+        calls.push(`remove:${id}`);
+      },
+    },
+    { id: 'overlay-loading-status', dismiss: true },
+  );
+
+  assert.deepEqual(calls, ['remove:overlay-loading-status']);
+});