feat(subtitles): add local Japanese subtitle generation

- Generate Japanese SRTs through the overlay modal or launcher
- Support managed whisper.cpp models and optional dialogue detection

src/main/runtime/subtitle-generation-open.ts

@@ -0,0 +1,18 @@
+import { IPC_CHANNELS } from '../../shared/ipc/contracts';
+import { openOverlayHostedModal, retryOverlayModalOpen } from './overlay-hosted-modal-open';
+
+export function openSubtitleGenerationModal(
+  deps: Parameters<typeof openOverlayHostedModal>[0] & Parameters<typeof retryOverlayModalOpen>[0],
+): Promise<boolean> {
+  return retryOverlayModalOpen(deps, {
+    modal: 'subtitle-generation',
+    timeoutMs: 1500,
+    retryWarning: 'Subtitle generation modal did not acknowledge opening; retrying.',
+    sendOpen: () =>
+      openOverlayHostedModal(deps, {
+        channel: IPC_CHANNELS.event.subtitleGenerationOpen,
+        modal: 'subtitle-generation',
+        preferModalWindow: true,
+      }),
+  });
+}