Task #630: keep recipients list visible above iPad keyboard in Send Note

Problem: opening Send Note on iPad, tapping the search field opened the
soft keyboard which covered the recipients list and the Send button —
the dialog stayed centered on the full layout viewport.

Fix (artifacts/tx-os/src/components/notes/send-note-dialog.tsx):

Two-tier keyboard detection:
  1. Primary — `vv.keyboardInset > 0` from useVisualViewport. Works on
     desktop touch laptops, iPad Safari (regular tab), Android Chrome.
     When true, override DialogContent style with
       top = vv.offsetTop + vv.height/2 − 48 (QuickType inset)
       transform: translate(-50%, -50%)
     so the dialog recenters around the visible viewport region.
  2. Fallback — `searchFocused && matchMedia('(pointer: coarse)')`.
     Only used when visualViewport does NOT report an inset, which is
     the iPad PWA (Add to Home Screen) case explicitly called out in
     components/ui/dialog.tsx comment. Top-anchors at 6vh with
     maxHeight 50dvh so the dialog never crosses the screen midpoint.
  3. Neither — pass NO style at all so Radix's default centered layout
     is fully restored (no leftover transition or top).

Touch-only fallback gating (matchMedia pointer:coarse) prevents the
earlier desktop-regression flagged by code review — focusing the
search on a desktop never repositions the dialog.

Other changes:
- onFocus/onBlur on the search input feed the fallback signal.
- Blur is debounced 150ms so tapping a recipient row mid-blur doesn't
  recenter the dialog out from under the finger.
- useEffect cleanup clears pending blur timeout on unmount.

Verification: tsc clean. Architect approved the touch-gated fallback;
follow-up review reconciled the diff with the spec's primary
visualViewport-driven path.

artifacts/tx-os/src/components/notes/send-note-dialog.tsx

@@ -120,14 +120,22 @@ export function SendNoteDialog({
     }, 150);
   };
 
+  // Primary signal: visualViewport actually reports a keyboard inset.
+  // Used on desktop touch laptops, iPad Safari (regular tab), and
+  // Android Chrome where vv updates correctly.
+  const keyboardActive = vv.keyboardInset > 0;
+  // Fallback signal: iPad PWA (Add to Home Screen) doesn't reliably
+  // update visualViewport when the keyboard opens (see comment in
+  // components/ui/dialog.tsx). On touch-primary devices, treat focus
+  // on the search input as evidence the keyboard is up so the dialog
+  // still gets repositioned. This is a fallback only — when vv DOES
+  // update, the primary branch above takes over.
+  const keyboardFallback = !keyboardActive && searchFocused && isTouchPrimary;
   const KEYBOARD_PREDICTION_INSET =
-    vv.keyboardInset > 0 || keyboardLikely ? 48 : 0;
+    keyboardActive || keyboardFallback ? 48 : 0;
   const listMaxHeight = (() => {
-    // Only assume the ~50% usable bound on touch devices where a
-    // soft keyboard is actually about to appear. Desktops keep using
-    // the real viewport height (or visualViewport when it updates).
     const baseHeight = vv.height || window.innerHeight;
-    const assumedUsable = keyboardLikely
+    const assumedUsable = keyboardFallback
       ? Math.min(baseHeight, window.innerHeight * 0.5)
       : baseHeight;
     const usable = assumedUsable - KEYBOARD_PREDICTION_INSET;
@@ -139,20 +147,32 @@ export function SendNoteDialog({
     return forList;
   })();
 
-  // Override DialogContent's centered positioning while typing on
-  // touch devices: anchor to top with `translate(-50%, 0)` so the
-  // dialog grows downward from a fixed top edge and never extends
-  // past the midpoint of the screen (where the soft keyboard sits).
-  // On desktop and other non-touch contexts, leave Radix's default
-  // centered layout alone.
-  const dialogStyle: React.CSSProperties = keyboardLikely
+  // Dialog positioning override:
+  //   • Primary path (`keyboardActive`): compute the new vertical
+  //     centre from the *visual* viewport — anchored at
+  //     `offsetTop + height/2`, shifted up by the QuickType strip
+  //     allowance so the Send button isn't hidden under predictions.
+  //     Keep Radix's `translate(-50%, -50%)` so the dialog stays
+  //     centered around the new anchor.
+  //   • Fallback path (`keyboardFallback`): top-anchor at 6vh with
+  //     `translate(-50%, 0)` and cap `maxHeight: 50dvh` so the dialog
+  //     never crosses the screen midpoint where the keyboard sits.
+  //   • Otherwise: pass NO style so Radix's default centered layout
+  //     is fully restored (no leftover transition, no leftover top).
+  const dialogStyle: React.CSSProperties | undefined = keyboardActive
+    ? {
+        top: vv.offsetTop + vv.height / 2 - KEYBOARD_PREDICTION_INSET,
+        transform: "translate(-50%, -50%)",
+        transition: "top 120ms ease",
+      }
+    : keyboardFallback
       ? {
           top: "6vh",
           transform: "translate(-50%, 0)",
           maxHeight: "50dvh",
           transition: "top 120ms ease, transform 120ms ease",
         }
-    : { transition: "top 120ms ease, transform 120ms ease" };
+      : undefined;
 
   const candidates = useMemo(() => {
     const me = user?.id;
@@ -217,7 +237,7 @@ export function SendNoteDialog({
     <Dialog open onOpenChange={(o) => !o && onClose()}>
       <DialogContent
         className="max-w-md"
-        style={dialogStyle}
+        {...(dialogStyle ? { style: dialogStyle } : {})}
         data-testid="send-note-dialog"
       >
         <DialogHeader className="pr-8">