ui: round 5 — AGENT'S THINKING buys the 3ch rail; the standard chord; dashed model names

- THE 3CH RAIL: 'AGENT’S THINKING' (16ch, flush) − 'YOUR THINKING' (13ch)
  = 3ch of mono — the rail widens to 3ch (border + padding), keeping the
  chevrons aligned while giving the quote room to breathe (the 1ch rail
  read cramped). YOU row follows.
- THE STANDARD CHORD everywhere: Enter submits, Shift+Enter is a
  newline, ⌘/Ctrl+Enter works too — the teaching thinking field drops
  the ⌘-only Gmail convention; the hint reads '↵ submits · ⇧↵ newline'
  in both docks, shown in text mode too (it Enter-submits as well).
- The transcript-end optimistic placeholder joins the register: small
  mono caps THINKING… (was text-sm sentence case).
- Model names keep their dashes: prettyModel renders 'glm-5.3-flash'
  exactly as written (no auto-caps, no dash→space join).

components/ai-elements/reasoning.tsx

@@ -137,7 +137,7 @@ const defaultGetThinkingMessage = (isStreaming: boolean) => {
   if (isStreaming) {
     return <Shimmer duration={1}>Thinking...</Shimmer>;
   }
-  return <p>AGENT THINKING</p>;
+  return <p>AGENT’S THINKING</p>;
 };
 
 export const ReasoningTrigger = memo(