fix(dashboard): allow textarea taps + resync iOS keyboard on page restore

Two fixes for residual mobile chat issues:

1) Textarea touch-action: none was preventing iOS from registering a
   clean tap-to-focus, causing the keyboard to flash up via the
   programmatic focus() in onTouchStart and then auto-dismiss because
   iOS never saw the gesture complete. Switching to manipulation
   allows tap while still blocking pan/zoom — the composer stays
   anchored thanks to overscroll-behavior: contain on its container.

2) On switch-away-and-back the visualViewport metrics could get
   stuck in a half-state (composer pushed up, or blank pane covering
   it). Adding a visibilitychange / pageshow handler on ChatView that
   force-blurs and re-focuses the active textarea makes iOS resync
   the keyboard / vv metrics cleanly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/ChatView.css

@@ -848,14 +848,12 @@
   line-height: 1.4;
   max-height: 120px;
   min-height: 40px;
-  /* iOS: any pan-y gesture on the textarea (including pan-y itself)
-     can drive an auto-scroll-into-view that lifts the composer up
-     off-screen even with body locked. touch-action: none blocks
-     gesture-driven panning while keeping tap-to-focus and typing
-     intact. Trade-off: loses gesture scroll within the textarea once
-     content exceeds max-height (~6 lines); arrow keys / caret moves
-     still work. */
-  touch-action: none;
+  /* touch-action: manipulation allows tap-to-focus (so iOS doesn't
+     auto-dismiss the keyboard between gesture frames) and blocks
+     double-tap zoom + pan/zoom gestures. We previously tried `none`
+     to lock the composer against pan, but that broke first-tap
+     focus on iOS. */
+  touch-action: manipulation;
   overscroll-behavior: contain;
 }