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/graph-context-marker.tsx

@@ -91,7 +91,7 @@ export function GraphContextList({ data }: { data: GraphContextData }): ReactNod
 					<li key={p.id} className="flex items-baseline gap-2">
 						<span className="shrink-0 tabular-nums text-muted-foreground">{i + 1}.</span>
 						{p.level && (
-							<span className="shrink-0 rounded bg-foreground/10 px-1 py-0.5 text-xxs text-muted-foreground">
+							<span className="shrink-0 rounded bg-foreground/10 px-1 py-0.5 text-xs text-muted-foreground">
 								{p.level}
 							</span>
 						)}