feat(overlay): add loading OSD spinner and queue notifications until ren

- Show mpv OSD spinner from start-file until subminer-overlay-loading-ready; force-shown for visible-overlay startup regardless of osd_messages setting
- Gate non-macOS overlay visibility on content-ready so first subtitle line is immediately hoverable and clickable
- Queue startup notifications in main process until overlay window finishes loading; upsert progress cards by id to avoid cold-start floods
- Defer background warmups until after overlay runtime init so queued notifications can deliver promptly
- Preserve character dictionary checking/building/importing/ready phases as distinct history entries; route building and importing to system notifications when notificationType is both

src/renderer/renderer-init-order.test.ts

@@ -58,6 +58,22 @@ test('renderer reports subtitle bounds immediately after initial subtitle layout
   assert.ok(immediateMeasurementIndex < listenerIndex);
 });
 
+test('renderer wires subtitle pointer handlers before first subtitle paint', () => {
+  const primaryMouseEnterIndex = indexOfRequired(
+    "ctx.dom.subtitleContainer.addEventListener('mouseenter', mouseHandlers.handlePrimaryMouseEnter);",
+  );
+  const pointerTrackingIndex = indexOfRequired('mouseHandlers.setupPointerTracking();');
+  const initialRenderIndex = indexOfRequired('subtitleRenderer.renderSubtitle(initialSubtitle);');
+  const initialMeasurementIndex = indexOfRequired(
+    'positioning.applyYPercent(positioning.getCurrentYPercent());\n  measurementReporter.emitNow();',
+  );
+
+  assert.ok(primaryMouseEnterIndex < initialRenderIndex);
+  assert.ok(pointerTrackingIndex < initialRenderIndex);
+  assert.ok(primaryMouseEnterIndex < initialMeasurementIndex);
+  assert.ok(pointerTrackingIndex < initialMeasurementIndex);
+});
+
 test('renderer reports subtitle bounds immediately after live subtitle layout', () => {
   const liveRenderIndex = indexOfRequired('subtitleRenderer.renderSubtitle(data);');
   const liveLayoutIndex = indexOfRequired(