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/main/runtime/overlay-notification-position.test.ts

@@ -0,0 +1,24 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { withConfiguredOverlayNotificationPosition } from './overlay-notification-position';
+
+test('overlay notification payloads inherit configured overlay position', () => {
+  assert.deepEqual(
+    withConfiguredOverlayNotificationPosition(
+      { title: 'SubMiner', body: 'Ready' },
+      { notifications: { overlayPosition: 'top' } },
+    ),
+    { title: 'SubMiner', body: 'Ready', position: 'top' },
+  );
+});
+
+test('overlay notification payload position can override configured position', () => {
+  assert.deepEqual(
+    withConfiguredOverlayNotificationPosition(
+      { title: 'SubMiner', body: 'Ready', position: 'top-left' },
+      { notifications: { overlayPosition: 'top-right' } },
+    ),
+    { title: 'SubMiner', body: 'Ready', position: 'top-left' },
+  );
+});