ui: plan canvas ink extent + the keyboard-first round

Plan canvas (owner report: arrows clipped at the viewBox edge in dist —
measured 14px/20px cuts in the owner's real plans): blockLayout now
unions node boxes with every edge path's control-point hull (a bezier
never leaves it; the layout calls edgePathD with the renderer's exact
inputs). Dagre's node extent stays the floor, so ordinary plans render
byte-identical; the viewBox origin shifts only when ink bulges past
zero. Verified on both real chats; pins use the owner's real
linear-algebra tree (golden-real-data).

Keyboard-first (owner's law: Enter always submits, arrows always cycle;
text fields the only exception):
- Enter guard split (enter-submits): a focused BUTTON keeps native
  Enter only when keyboard-walked (:focus-visible) or inside an open
  overlay (menus/dialogs); pointer-clicked transcript buttons submit,
  preventDefault suppressing the re-activation underneath.
- Focus hygiene (focus-hygiene): pointer clicks on transient controls
  (agent/user thinking toggles, copy, mermaid expand, plan chip) blur
  to body — the state clicking empty space produces.
- Session search owns the walk: Up/Down wrap-cycle the filtered rows,
  Enter opens the walked row or the first match (quick-open), then
  blurs and keeps the query. The Alt-arrow session cycle is RETIRED.
- Registry: model-menu walk/pick entries removed (obvious in-field
  navigation, not settings material); question-dock keys stay
  displayOnly per owner ruling.

Gates: 1489/1489, typecheck, lint. Verified live end-to-end.

components/chat.tsx

@@ -24,6 +24,7 @@ import { artifactRenderers } from "@/components/artifacts";
 import { SubagentSteerCard } from "@/components/artifacts/steer-card";
 import { Composer } from "@/components/composer";
 import { useEnterSubmits } from "@/components/enter-submits";
+import { blurAfterPointerClick } from "@/components/focus-hygiene";
 import { dockStateKey } from "@/components/dock-state-key";
 import { QueuedSteersBody, type QueuedSteerLine } from "@/components/queued-steers";
 import { DictationBar, finishDictation, joinDictation, useDictation } from "@/components/dictation";
@@ -1264,7 +1265,10 @@ export function Chat({
 <button
 							type="button"
 							data-testid="plan-chip"
-							onClick={() => setPlanOpen(true)}
+							onClick={(e) => {
+								blurAfterPointerClick(e);
+								setPlanOpen(true);
+							}}
 							className="lh-no-drag flex shrink-0 cursor-pointer items-center gap-1.5 rounded-full border border-border/80 px-2 py-0.5 text-xs font-medium uppercase tracking-wide text-muted-foreground transition-colors hover:border-border hover:text-foreground"
 						>
 							<WaypointsIcon className="size-3.5 text-primary" aria-hidden />