Stop phones zooming when a field is focused

- Viewport: maximum-scale=1 and user-scalable=no (app-like, no pinch or
  double-tap zoom on phones).
- Mobile-only rule keeps every input/textarea/select at 16px so iOS
  Safari's focus auto-zoom never triggers (it ignores user-scalable=no for
  that). Deliberately unlayered so it beats the per-component Tailwind
  sizes; desktop keeps the designed 12-14px fields.

New zoom suite (6 checks): viewport meta, gate input, settings key input,
notes textarea and every study-feed field at >= 16px on a phone, desktop
sizes unchanged. Install sheet 64/64, pwa 16/16, final-ux 12/12,
security 8/8, contrast 20/20.

README.md

@@ -777,6 +777,10 @@ Things I chose while building, with the reasoning:
     device, uses Chrome's deferred `beforeinstallprompt` for a one-tap install where available, and
     stays reachable from Settings. It is mounted in the root layout, so it can appear over any
     screen — including the key gate — without blocking the page underneath.
+30. **Phones don't zoom, and mobile fields are 16px.** The viewport sets `maximum-scale=1` /
+    `user-scalable=no` for an app-like feel, and a mobile-only rule keeps every input and textarea at
+    16px so iOS Safari's focus auto-zoom never fires (iOS ignores `user-scalable=no` for that).
+    Desktop keeps the designed 12–14px field sizes.
 14. **`gpt-oss:120b` does all content work — but it cannot read images** (`this model does not
     support image input`), so `VISION_MODEL` has to stay a multimodal model (`gemma4:31b-cloud`).
     Text-only inputs — pasted text, PDFs with a text layer, DOCX/PPTX/ODT — never touch the vision