ui: the unified ThinkingBlock — one visual language for the learner's thinking

Owner round (2026-10-05): the same act (a human thinking in text) had two
visual languages — the quiz cards' quote block vs the practice container
with a collapsing chevron and raw pre-wrap text that read oversized.

- components/thinking-block.tsx: the quiz quote-block recipe verbatim
  (rail + uppercase label + lh-prose at foreground/90) carried by a
  faint user-side shell — ml-auto, max-w-[95%] mirroring the user
  bubble's geometry, px-4/py-3 rhythm. Never collapsible. Rails reuse
  the existing vocabulary: primary = committed register, muted =
  working register.
- ThinkingCard becomes the practice adapter: 'Your solution' (primary)
  / 'Your thinking' (muted) — one component, two registers.
- The reading channel LIFTS out of the answered card: chronologically
  prior to the question, it renders above it as its own user-side
  block under the plain 'Your thinking' label; the in-card inset and
  the 'while reading' phrasing are gone.
- lh-card-enter (globals.css): the one-shot 150ms fade+rise mount,
  the app's motion register; honors reduced-motion.

app/globals.css

@@ -530,3 +530,29 @@ body {
 @theme {
 	--font-title: "lh-cmu", serif;
 }
+
+/* Card enter (owner round, 2026-10-05): the transcript cards' one-shot
+   mount — a subtle fade + 4px rise, the app's motion register (150ms,
+   dock-variant/settings-pop taste). Nothing on update, nothing on
+   unmount. Applied by the unified ThinkingBlock and the practice
+   cards; honors reduced-motion by appearing. */
+@keyframes lh-card-enter {
+	from {
+		opacity: 0;
+		transform: translateY(4px);
+	}
+	to {
+		opacity: 1;
+		transform: translateY(0);
+	}
+}
+
+.lh-card-enter {
+	animation: lh-card-enter 150ms ease-out;
+}
+
+@media (prefers-reduced-motion: reduce) {
+	.lh-card-enter {
+		animation: none;
+	}
+}