feat: keyboard shortcuts wave A — registry, provider, global bindings

The shortcut architecture (owner-approved plan, 2026-09-17):
- src/keyboard.ts: pure action registry (id, label, scope, default
  binding) + lh:keymap localStorage overrides + event normalization.
  The settings milestone renders this same registry as its editor.
- components/keyboard-shortcuts.tsx: the single document-level keydown
  listener (window level, bubble) owning the pieces no surface owns:
  - Tab is DEAD (owner decision): browser tab-focus navigation is
    abandoned; Tab is suppressed everywhere, Shift+Tab cycles the
    thinking level.
  - Esc is a layered dismiss: topmost popover first (popovers
    stopPropagation their own Esc — usePopoverDismiss + ModelControl),
    then dictation stop (lh:kbd-stop-dictation), then abort of an
    in-flight turn (lh:kbd-abort-turn; server-side wake turns are
    honestly non-stoppable — the seam only stops local streams).
  - Global actions dispatch lh:kbd-<action> window events (the
    lh:chat-renamed pattern); surfaces that aren't mounted simply
    don't listen.
- The input guard: inside a typing surface only mod/alt combos (and
  Tab) fire; bare keys pass through to the field.
- Cheat sheet overlay (?) renders from the registry, grouped by scope.

Bindings wired this wave: cmd+d dictation toggle, cmd+k model picker,
shift+tab thinking cycle, cmd+b sidebar, cmd+shift+f sessions search,
alt+up/down + alt+enter session cycling, cmd+g graph view, cmd+n new
session, f2 rename (chat), ? cheat sheet. Wave B adds the question
keyboard machine; wave C the per-surface bindings (find, import).

Verified live in the dev shell (CDP): all of the above via
Input.dispatchKeyEvent.

Co-Authored-By: Claude Fable 4.5 plus-plus <noreply@anthropic.com>

components/model-picker.tsx

@@ -127,7 +127,12 @@ export function ModelControl({
 			}
 		};
 		const onKeyDown = (e: KeyboardEvent) => {
-			if (e.key === "Escape") setOpen(null);
+			if (e.key === "Escape") {
+				// Claim the Esc (keyboard wave A): the window-level chain must
+				// not ALSO stop dictation / abort the turn under this menu.
+				e.stopPropagation();
+				setOpen(null);
+			}
 		};
 		document.addEventListener("pointerdown", onPointerDown);
 		document.addEventListener("keydown", onKeyDown);
@@ -168,6 +173,30 @@ export function ModelControl({
 		[chatId, onSaved],
 	);
 
+	// Shortcut seams (keyboard wave A): ⌘K opens the model menu (the
+	// universal command convention); Shift+Tab cycles the thinking level
+	// up the ladder (wrapping) — the owner's replacement for browser
+	// tab-focus. Both work from any focus, including mid-typing.
+	useEffect(() => {
+		const onOpenPicker = () => {
+			setOpen("model");
+			setQuery("");
+			setError(null);
+		};
+		window.addEventListener("lh:kbd-open-model-picker", onOpenPicker);
+		return () => window.removeEventListener("lh:kbd-open-model-picker", onOpenPicker);
+	}, []);
+
+	useEffect(() => {
+		const onCycleThinking = () => {
+			if (levels.length === 0) return;
+			const idx = effectiveLevel === undefined ? -1 : levels.indexOf(effectiveLevel);
+			void save({ ...(settings ?? {}), thinkingLevel: levels[(idx + 1) % levels.length] });
+		};
+		window.addEventListener("lh:kbd-cycle-thinking", onCycleThinking);
+		return () => window.removeEventListener("lh:kbd-cycle-thinking", onCycleThinking);
+	}, [levels, effectiveLevel, save, settings]);
+
 	// The filtered, ranked model list.
 	const results = (catalog?.models ?? [])
 		.map((m) => ({ m, s: fuzzyScore(query, m.provider, m.id, m.name) }))