Typography round 4 (owner): the snap to the ladder — prose 16.5→16, xxs rung merged into xs

The system: the ladder is the truth, everything snaps to it.

- Prose snaps to the ladder's 16px rung (--lh-prose-size 16.5→16; the
  half-pixel was a reskin-era hand-tune with no visible payoff and a
  system cost). lh-prose, lh-input, and the session titles all read the
  one variable — one reading size, now a ladder citizen. @theme inline
  inlines literals without emitting runtime vars, so the variable can't
  var()-link to --text-lg: documented as the one deliberate duplication
  (change one, change both).
- The 10px rung merges into 11px: one pixel apart was a distinction with
  no visible difference, and 10px sits at the mono legibility floor —
  quiet labels (Sessions, Background agents, dock hints, model-picker
  footers) get their quiet from color + tracking, not a notch of size.
  All 13 text-xxs uses → text-xs; --text-xxs token removed.
- Derived constant follows: TEXT_CAP_SCALE 16.5/12.5 → 16/12.5 (1.32 →
  1.28; test pin 232.32px → 225.28px) — the plan-graph text cap now
  tracks the snapped prose size.

Live: title 16px, Sessions/Background-agents labels 11px, composer 16px
with the 20px lh-input line box. Gates: typecheck, lint, 469/469.

Lane note: components/graph-context-marker.tsx (graph-stream file) had a
mechanical text-xxs → text-xs swap — required: the token removal
otherwise leaves a dead class in their file.

components/answered-card.tsx

@@ -72,7 +72,7 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 										)}
 									>
 										{/* Owner round 8: a touch smaller than the text (size-4→size-3.5,
-											   ≈14px vs the 16.5px row) while centered. */}
+											   ≈14px vs the 16px row) while centered. */}
 										{(key || sel) && <GlyphMark kind={key ? "check" : "x"} className="size-3.5" />}
 									</span>
 								)}
@@ -101,7 +101,7 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 
 			{answer.note && (
 				<div data-testid="your-thinking" className="mt-3 border-l-2 border-primary/40 pl-3">
-					<span className="mb-0.5 block text-xxs font-medium uppercase tracking-wide text-muted-foreground">
+					<span className="mb-0.5 block text-xs font-medium uppercase tracking-wide text-muted-foreground">
 						Your thinking
 					</span>
 					<span className="lh-prose block whitespace-pre-wrap text-foreground/90">{answer.note}</span>