fix(intro): splash always honors App's decision + video streams 3x lighter

- SplashScreen no longer re-checks neode_intro_seen itself: it silently
  skipped the whole logo-tap/typing sequence for any browser that had
  seen the intro before, even when App.vue explicitly requested it (demo
  fresh visits, Replay Intro). App.vue is the single decision point.
- Intro video re-encoded 12.7MB/12.6Mbps → 4.3MB/4.2Mbps (1920x1080 CRF23
  faststart, muted track dropped) — visually identical on this
  illustrated content; cache-buster bumped to v=8.
- Video is <link rel=preload>ed the moment the splash is scheduled (the
  <video> element only mounts ~20s in, so cold caches used to start the
  download mid-sequence and stutter).
- nginx demo cache regex now covers mp4/webm/mp3/webp/woff2 so repeat
  visits play from browser cache.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/views/OnboardingWrapper.vue

@@ -17,7 +17,7 @@
         @pause.prevent="handleVideoPause"
         @ended="handleVideoEnded"
       >
-        <source src="/assets/video/video-intro.mp4?v=7" type="video/mp4">
+        <source src="/assets/video/video-intro.mp4?v=8" type="video/mp4">
       </video>
       
       <!-- Login: static background + archipelago-style glitch (no zoom) -->