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/utils/dom.ts

@@ -2,6 +2,7 @@ export type RendererDom = {
   subtitleRoot: HTMLElement;
   subtitleContainer: HTMLElement;
   overlay: HTMLElement;
+  overlayNotificationStack: HTMLDivElement;
   controllerStatusToast: HTMLDivElement;
   overlayErrorToast: HTMLDivElement;
   secondarySubContainer: HTMLElement;
@@ -132,6 +133,7 @@ export function resolveRendererDom(): RendererDom {
     subtitleRoot: getRequiredElement<HTMLElement>('subtitleRoot'),
     subtitleContainer: getRequiredElement<HTMLElement>('subtitleContainer'),
     overlay: getRequiredElement<HTMLElement>('overlay'),
+    overlayNotificationStack: getRequiredElement<HTMLDivElement>('overlayNotificationStack'),
     controllerStatusToast: getRequiredElement<HTMLDivElement>('controllerStatusToast'),
     overlayErrorToast: getRequiredElement<HTMLDivElement>('overlayErrorToast'),
     secondarySubContainer: getRequiredElement<HTMLElement>('secondarySubContainer'),