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/question-dock.tsx

@@ -387,7 +387,7 @@ function QuestionDockForm({
 										setSel((prev) => (prev.otherSelected ? prev : toggleOther(selectMode, prev)));
 									}}
 									placeholder="Type your own answer…"
-									className="lh-prose w-full min-w-0 flex-1 bg-transparent outline-none placeholder:text-muted-foreground"
+									className="lh-input w-full min-w-0 flex-1 bg-transparent outline-none placeholder:text-muted-foreground"
 									onClick={(e) => e.stopPropagation()}
 								/>
 							</div>
@@ -429,7 +429,7 @@ function QuestionDockForm({
 							}}
 							placeholder="Type your answer…"
 							rows={1}
-							className="field-sizing-content lh-prose max-h-48 min-h-10 w-full 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 w-full resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
 						/>
 					) : (
 						<textarea
@@ -446,7 +446,7 @@ function QuestionDockForm({
 							placeholder="Why this answer? What are you unsure about? Say as much as you like — the teacher reads all of this."
 							rows={1}
 							className={cn(
-								"field-sizing-content lh-prose max-h-48 w-full resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground/70",
+								"field-sizing-content lh-input max-h-48 w-full resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground/70",
 								// Phase-scaled prominence: teaching invites depth,
 								// probing stays quick.
 								phase === "teach" ? "min-h-[4.5rem]" : "min-h-10",