ui: consistency sweep — the 1ch rail geometry, Submit thinking, no auto-caps

Owner round 4 (2026-10-05):

- THE RAIL IS THE MISSING CHARACTER: rail + padding = exactly 1ch of
  the mono heading font. 'YOUR THINKING' (13ch) + rail == 'AGENT
  THINKING' (14ch) flush — the chevrons line up vertically, no fixed
  columns. The YOU heading joins the rail (label inside, like the
  thinking rows) — one quote geometry everywhere.
- HEADING REGISTER: YOUR THINKING / AGENT THINKING / YOU all use the
  card eyebrows' small mono caps (text-xs = the 11px rung, font-medium
  uppercase tracking-wide) — the app chrome is JetBrains Mono.
- SUBMIT THINKING: the practice button is now literally the question
  dock's Button (h-9, px-3.5) in one p-1 row with the hint left
  ('↵ submits · ⇧↵ newline') — the keyboard hints are back. Corner
  radii concentric in both docks: shell 16 − 6 = field 10 − 4 = button 6
  (rounded-[10px] fields, rounded-[6px] buttons — the old rounded-xl/12
  was the 'too large' culprit).
- MODEL NAMES: prettyModel no longer auto-capitalizes — names render
  exactly as their providers write them ('glm 5.3 flash').
- Quiz explanations pulled closer (mt-3 → mt-2).

components/answered-card.tsx

@@ -150,7 +150,7 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 				   verdict shows, but the explanation sits collapsed — viewable,
 				   never center stage. The teaching that follows resolves the
 				   prediction; THAT is the real explanation. */
-				<div className="mt-3" data-testid="tucked-explanation">
+				<div className="mt-2" data-testid="tucked-explanation">
 					<button
 						type="button"
 						onClick={() => setWhyOpen((v) => !v)}
@@ -168,7 +168,7 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 			) : (
 				isQuiz &&
 				answer.explanation && (
-					<div className="mt-3 rounded-lg bg-muted py-2 text-sm text-foreground/50">
+					<div className="mt-2 rounded-lg bg-muted py-2 text-sm text-foreground/50">
 						<span className="font-medium text-muted-foreground">Why: </span>
 						{/* The markdown wrapper must go truly inline — a block <p> after the
 						   "Why:" label created the oversized leading gap (owner's fix list). */}