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/sidebar.tsx

@@ -138,7 +138,7 @@ export function SessionRow({
 				    the meta line below stays JetBrains Mono (machine data). One
 				    rule, finally applied to the picker too (owner, typography
 				    round): mono = chrome, Source Sans = human words. */}
-				<span className="block truncate font-prose">{chat.title}</span>
+				<span className="block truncate font-prose text-base">{chat.title}</span>
 				<span className="block text-xs text-muted-foreground">{sessionMeta(chat)}</span>
 			</span>
 		</button>