Approval cards show again: the buttons no longer throw, the command is the item's detail

An agent chat's bash approval left "Waiting for you to allow bash…" with no card: cardOf()
called append(actions, a, b, c) while append() took one array, so `children.flat` threw for
every approval and plan card (questions used el.append and worked). renderCards() had already
unhidden #cards, which stayed empty. append() now takes children as rest arguments too.

- The editable command is `detail` (services/device_link.py puts the fixed "Run a command" in
  the title); it is sent back as the item's text only when changed. Non-editable approvals
  show the title and the device's input. `purpose` ("It says: …"), `reason` and the asking
  subagent (`job`) are shown, as on the web page.
- renderCards() keeps a card already on the screen (by id) instead of drawing every card again
  on each `ask` frame, which the server re-sends whenever the countdown changes; a card that
  cannot be drawn shows the error instead of an empty box.
- tests/ui/: headless harness with a mocked Tauri bridge; five A1 cases (device bash card
  shows and is visible, Allow/edit/Deny post to /chats/{id}/interactions/{card}, redraw keeps
  edits, reopen gets the card from the stream's first pass, 390 px).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ui/js/dom.js

@@ -27,7 +27,8 @@ export function h(tag, attrs, ...children) {
   return el
 }
 
-export function append(el, children) {
+/** append(el, child, [more], …): children one by one or in arrays, nested as deep as they come. */
+export function append(el, ...children) {
   for (const c of children.flat(Infinity)) {
     if (c === null || c === undefined || c === false) continue
     el.append(c instanceof Node ? c : document.createTextNode(String(c)))