feat: YC application answers + Remotion video component + gitignore updates

- Add YC_APPLICATION_ANSWERS.md with full Summer 2026 application draft
  (all fields answered, updated with mortgage broker user interview quote)
- Wire OffthreadVideo into YCAppVideo.tsx for founder recording playback
- Ignore .mov files and .gstack/ in .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -19,3 +19,6 @@ opencode.json
 videos/remotion-demo/node_modules
 videos/remotion-demo/build
 videos/remotion-demo/out
+videos/remotion-demo/public/*.mov
+product/*.mov
+.gstack/