feat: integrate n+1 target highlighting

- Merge feature branch changes for n+1 target-only highlight flow

- Extend merged token model and token-merger to mark exactly-one unknown targets

- Thread n+1 candidate metadata through tokenizer and config systems

- Update subtitle renderer/state to route configured colors and new token class

- Resolve merge conflicts in core service tests, including subtitle and subsync behavior

src/core/services/overlay-bridge-service.test.ts

@@ -12,17 +12,17 @@ test("sendToVisibleOverlayRuntimeService restores visibility flag when opening h
   let visibleOverlayVisible = false;
 
   const ok = sendToVisibleOverlayRuntimeService({
-      mainWindow: {
-        isDestroyed: () => false,
-        webContents: {
-          isLoading: () => false,
-          send: (...args: unknown[]) => {
-            sent.push(args);
-          },
+    mainWindow: {
+      isDestroyed: () => false,
+      webContents: {
+        isLoading: () => false,
+        send: (...args: unknown[]) => {
+          sent.push(args);
         },
-      } as unknown as Electron.BrowserWindow,
+      },
+    } as unknown as Electron.BrowserWindow,
     visibleOverlayVisible,
-    setVisibleOverlayVisible: (visible) => {
+    setVisibleOverlayVisible: (visible: boolean) => {
       visibleOverlayVisible = visible;
     },
     channel: "runtime-options:open",