Add /set: on-set screen tracking markers for crews

- Unlinked, noindex page listing marker PNGs from public/set/markers
  (discovered at build time; filenames encode device/resolution/orientation)
- Detects the current screen and offers the closest match first
- One-tap full-screen viewer: wake lock, hidden controls, full grid/edges
  toggle, fill vs fit by aspect, back button closes, deep links via hash
- Offline service worker + home-screen manifest for iPhone full screen
- Marketing chrome moved into an (site) route group so /set has none

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -43,3 +43,6 @@ next-env.d.ts
 # source media (web versions live in public/)
 content/*.mp4
 content/*.pdf
+
+# source copies of screen markers (served from public/set/markers)
+content/screen_markers/