PWA for iPhone and iPad: PNG icons, splash screens, manifest; stay signed in for 180 days

- iOS ignores SVG touch icons: add 120/152/167/180 apple-touch-icons, 192/512 and maskable manifest icons,
  and 25 splash screens (every iPhone size, iPad portrait+landscape incl. 12.9")
- Icons and splash screens are public so iOS can fetch them without a session
- Manifest: id, scope, categories, shortcuts; iOS standalone polish (no callout, no overscroll)
- Sessions last SESSION_DAYS (default 180) and renew daily while in use
- tools/make-icons.py regenerates the artwork

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

public/sw.js

@@ -1,6 +1,6 @@
 // App-shell cache only; Seafile/API traffic always goes to the network.
-const CACHE = 'hub-v3';
-const SHELL = ['/', '/style.css', '/app.js', '/icon.svg', '/manifest.webmanifest'];
+const CACHE = 'hub-v4';
+const SHELL = ['/style.css', '/app.js', '/icon.svg', '/manifest.webmanifest', '/icons/icon-192.png', '/icons/apple-touch-icon.png'];
 
 self.addEventListener('install', e => {
   e.waitUntil(caches.open(CACHE).then(c => c.addAll(SHELL)));