/previz: password protect, add PDF export of the crowd previz

- nginx basic auth on /previz/ (login file lives on the server, mounted
  from docker/auth/, see DEPLOY.md step 8); private, no-store so
  Cloudflare never caches it
- Print styles for previz pages: dark, A4 landscape, one section a page;
  videos print as poster frames with a link
- scripts/previz-pdf.mjs (npm run previz:pdf) prints the page to
  public/previz/crowd/crowd-previz.pdf via Edge/Chrome DevTools
- "PDF" download link on the page

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

components/previz/ShotList.tsx

@@ -39,7 +39,7 @@ export default function ShotList({ shots, storeKey }: { shots: Shot[]; storeKey:
           <button
             type="button"
             onClick={() => setDone([])}
-            className="-my-2 py-2 font-mono text-[11px] tracking-[0.2em] text-muted uppercase hover:text-fg"
+            className="-my-2 py-2 font-mono text-[11px] tracking-[0.2em] text-muted uppercase hover:text-fg print:hidden"
           >
             Clear ticks
           </button>
@@ -78,7 +78,7 @@ export default function ShotList({ shots, storeKey }: { shots: Shot[]; storeKey:
           );
         })}
       </ul>
-      <p className="mt-3 text-xs text-muted">Ticks are saved on this device only.</p>
+      <p className="mt-3 text-xs text-muted print:hidden">Ticks are saved on this device only.</p>
     </div>
   );
 }