fix(mobile): app-feel pass — kill the website gestures

[bndct-devops]

The PWA felt like a website on phones (reported against Focus mode, but it applied app-wide): you could rubber-band the whole viewport past its edges, double-tap zoom, and long-press-select interface text — and the h-screen shell overhung the visible area behind mobile browser toolbars, which made the page itself pannable.

What

• html/body: overscroll-behavior: none (no edge bounce, no scroll chaining, no Android pull-to-refresh) + touch-action: manipulation (no double-tap zoom, taps fire without the legacy delay).
• Touch devices only (@media (pointer: coarse)): user-select: none + -webkit-touch-callout: none on interface chrome; input/textarea/[contenteditable] opt back into text selection. Desktop behavior is completely unchanged.
• App shells (AppShell, DashboardPage): h-screen → h-dvh so the shell matches the visible viewport under mobile browser toolbars; main scrollers get overscroll-contain.

Notes

• The EPUB reader renders inside its own iframe (foliate), so highlight-by-text-selection is unaffected by the chrome-level user-select: none.
• Pinch-zoom: the viewport meta (already present) handles Android and the installed iOS app; a regular iOS Safari tab always permits pinch for accessibility — nothing any site can do about that one.
• The reader already uses fixed inset-0, so it needed no dvh change.

Verification

• Emulated iPhone 13 viewport: all computed styles land (overscroll-behavior: none, touch-action: manipulation, chrome user-select: none with inputs back to text, main at contain, dvh root exactly matching innerHeight); desktop context confirmed at user-select: auto.
• Frontend npm run build (tsc) clean.
• The actual gesture feel (bounce/zoom on real hardware) needs a quick pass on your phone — emulation can't reproduce iOS gesture physics.

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Update (551dde1): a screen recording from the real device showed the actual headline symptom — the content area pans sideways and rubber-bands back. Root cause: WebKit counts the Focus rotary's pre-transform 540px stage as scrollable overflow (Chromium uses the post-transform size, which is why emulation initially missed it), giving the main scroller ~150px of horizontal scroll on a phone. Fixed by clamping the app's main scrollers with overflow-x-hidden; verified on Playwright WebKit (iPhone 13 viewport) that scrollLeft is pinned to 0.