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/question-dock.tsx

@@ -307,7 +307,7 @@ function QuestionDockForm({
 										)}
 									>
 										{isSel && (
-											<span className={cn(qd.mode === "multi-select" ? "text-xxs" : "size-1.5 rounded-full bg-current")}>
+											<span className={cn(qd.mode === "multi-select" ? "text-xs" : "size-1.5 rounded-full bg-current")}>
 												{qd.mode === "multi-select" ? "✓" : ""}
 											</span>
 										)}
@@ -373,7 +373,7 @@ function QuestionDockForm({
 									)}
 								>
 									{sel.otherSelected && (
-										<span className={cn(qd.mode === "multi-select" ? "text-xxs" : "size-1.5 rounded-full bg-current")}>
+										<span className={cn(qd.mode === "multi-select" ? "text-xs" : "size-1.5 rounded-full bg-current")}>
 											{qd.mode === "multi-select" ? "✓" : ""}
 										</span>
 									)}
@@ -412,7 +412,7 @@ function QuestionDockForm({
 					data-testid={qd.mode === "text" ? "answer-field" : "thinking-field"}
 					className="rounded-xl border border-border/70 bg-background/60 transition-colors focus-within:border-primary/50"
 				>
-					<div className="px-2.5 pt-2 text-xxs font-medium uppercase tracking-wide text-muted-foreground">
+					<div className="px-2.5 pt-2 text-xs font-medium uppercase tracking-wide text-muted-foreground">
 						{qd.mode === "text" ? "Your answer" : "Your thinking"}
 					</div>
 					{qd.mode === "text" ? (
@@ -455,7 +455,7 @@ function QuestionDockForm({
 					)}
 					<div className="flex items-center justify-between gap-2 p-1">
 						{qd.mode !== "text" && (
-							<span aria-hidden className="pl-1.5 text-xxs text-muted-foreground">
+							<span aria-hidden className="pl-1.5 text-xs text-muted-foreground">
 								⌘/Ctrl + ↵ submits
 							</span>
 						)}