Typography round 2 (owner): lh-input (caret at the font-metric floor) + 14px session titles

- lh-input: lh-prose's 1.5 reading leading made typing carets tower
  (~25px box on 16.5px text, ~2.1× the glyphs — the caret fills the line
  box in Chromium). Inputs are not paragraphs: 1.25 leading drops the
  caret to ~21px, the font-metric floor (as close to the glyphs as
  Chromium will draw). Swapped on every typing surface — composer
  (chat + home), the thinking field, answer + editable-Other inputs, the
  model search; rendered prose (message.tsx container, option
  descriptions, chat.tsx pre-wrap) keeps lh-prose 1.5. Same family and
  size as prose; only leading differs.
- Session titles: 14px (text-base) — Source Sans at 12.5px read as
  small as the 11px mono meta under them; the title now holds its rank.
  Live: title "Source Sans 3" 14px vs meta "JetBrains Mono" 11px, row
  52px; composer line box 20.625px (was 24.75px).

Gates: typecheck, lint, 469/469.

components/composer.tsx

@@ -59,7 +59,7 @@ export function Composer({
 				placeholder="Ask, answer, or steer the lesson…"
 				autoFocus={autoFocus}
 				rows={1}
-				className="field-sizing-content lh-prose max-h-48 min-h-10 flex-1 resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
+				className="field-sizing-content lh-input max-h-48 min-h-10 flex-1 resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
 			/>
 			{verdict && !busy ? (
 				// The plan verdict (docs/probe-teach-split.md §4): accept