Block pinch and double-tap zoom, including on iOS Safari

iOS Safari ignores user-scalable=no, so zoom is blocked in three layers:
- viewport meta: maximum-scale=1, user-scalable=no on every page
  (covers Android, home-screen apps and iOS focus zoom on inputs)
- CSS: touch-action: pan-x pan-y on html, so scrolling still works but
  pinch and double-tap zoom do not
- JS (fluid.js): cancel Safari's gesture* events and two-finger touchmove

Double-tap is left to CSS rather than JS so rapid repeated taps on
buttons still register as clicks.

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

public/create.html

@@ -2,7 +2,7 @@
 <html lang="ja">
 <head>
   <meta charset="utf-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
+  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no, viewport-fit=cover">
   <meta name="theme-color" media="(prefers-color-scheme: light)" content="#f2f2f7">
   <meta name="theme-color" media="(prefers-color-scheme: dark)" content="#000000">
   <meta name="robots" content="noindex, nofollow">