notes(ipad): keep dialog and inputs above the on-screen keyboard

Task #476. On iPad Safari, opening the keyboard while writing a new
note or replying inside the note thread dialog covered the bottom of
the dialog (textarea + send button). The dialog used
`top:50%; translate(-50%,-50%)` against the layout viewport and never
reacted to the visual viewport shrinking when the keyboard appeared.

Changes:
- artifacts/tx-os/index.html: added `interactive-widget=resizes-content`
  to the viewport meta so iOS 17+ resizes the layout viewport when the
  software keyboard opens.
- artifacts/tx-os/src/hooks/use-visual-viewport.ts: new hook that
  subscribes to `window.visualViewport` `resize` / `scroll` /
  `orientationchange` (rAF-throttled) and exposes the visible height,
  the visual viewport `offsetTop`, and the bottom keyboard inset.
- artifacts/tx-os/src/components/ui/dialog.tsx: `DialogContent` now
  reads the hook and, only when the keyboard inset exceeds ~80px,
  pins its center to `offsetTop + height/2` and caps `max-height` to
  the visible height. With the existing `translate(-50%,-50%)`, both
  edges stay inside the visible region above the keyboard. Desktop
  unaffected (inset is 0 → no inline style applied).
- artifacts/tx-os/src/pages/notes.tsx: thread reply textarea and the
  top composer textarea now call `scrollIntoView({ block: "center" })`
  on focus and again whenever the keyboard inset changes while the
  field is focused. Both paths are gated on `keyboardInset > 80`, so
  desktop focus is untouched.

Verification:
- `tsc --noEmit` clean.
- e2e: `notes-thread-dialog` and `notes-composer-color` both pass.

artifacts/tx-os/src/pages/notes.tsx

@@ -42,6 +42,7 @@ import { ar as dfAr, enUS as dfEn } from "date-fns/locale";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Textarea } from "@/components/ui/textarea";
+import { useVisualViewport } from "@/hooks/use-visual-viewport";
 import { Badge } from "@/components/ui/badge";
 import {
   AlertDialog,
@@ -2228,6 +2229,16 @@ function ThreadDialog({
   const markedRef = useRef(false);
   const replyInputRef = useRef<HTMLTextAreaElement | null>(null);
   const focusedRef = useRef(false);
+  const replyFocused = useRef(false);
+  const { keyboardInset } = useVisualViewport();
+  // When the on-screen keyboard appears while the reply box is focused,
+  // pull the cursor into the centre of the visible viewport. Gated on a
+  // non-trivial inset so desktop focus is unaffected.
+  useEffect(() => {
+    if (keyboardInset <= 80) return;
+    if (!replyFocused.current) return;
+    replyInputRef.current?.scrollIntoView({ block: "center" });
+  }, [keyboardInset]);
 
   // When opened from the incoming-note popup with reply intent, jump
   // focus into the reply input as soon as the thread loads.
@@ -2410,6 +2421,15 @@ function ThreadDialog({
                   ref={replyInputRef}
                   value={replyText}
                   onChange={(e) => setReplyText(e.target.value)}
+                  onFocus={(e) => {
+                    replyFocused.current = true;
+                    if (keyboardInset > 80) {
+                      e.currentTarget.scrollIntoView({ block: "center" });
+                    }
+                  }}
+                  onBlur={() => {
+                    replyFocused.current = false;
+                  }}
                   placeholder={t("notes.replyPlaceholder", "Write a reply…")}
                   className="min-h-[70px] resize-none"
                   data-testid="thread-reply-input"
@@ -2886,6 +2906,17 @@ function Composer({
   const targetFolderId =
     folderSelection.kind === "folder" ? folderSelection.id : null;
   const ref = useRef<HTMLDivElement>(null);
+  const contentRef = useRef<HTMLTextAreaElement | null>(null);
+  const contentFocused = useRef(false);
+  const { keyboardInset } = useVisualViewport();
+  // Same keyboard-aware scroll-into-view as the thread reply box: only
+  // fires while a software keyboard is actually open and the composer
+  // textarea is focused. Desktop focus is unaffected.
+  useEffect(() => {
+    if (keyboardInset <= 80) return;
+    if (!contentFocused.current) return;
+    contentRef.current?.scrollIntoView({ block: "center" });
+  }, [keyboardInset]);
 
   useEffect(() => {
     if (!open) return;
@@ -3012,8 +3043,18 @@ function Composer({
             </div>
           ) : (
             <Textarea
+              ref={contentRef}
               value={content}
               onChange={(e) => setContent(e.target.value)}
+              onFocus={(e) => {
+                contentFocused.current = true;
+                if (keyboardInset > 80) {
+                  e.currentTarget.scrollIntoView({ block: "center" });
+                }
+              }}
+              onBlur={() => {
+                contentFocused.current = false;
+              }}
               placeholder={t("notes.contentPlaceholder", "Take a note...")}
               className="border-0 bg-transparent shadow-none focus-visible:ring-0 px-1 mt-1 min-h-[80px] resize-none"
               data-testid="notes-composer-content"