Fix ⌘B: dispatch/listen event-name mismatch; thinking pill → "Thinking (⇧⇥)"

Root cause (interlude, owner 2026-09-25): keyboard-shortcuts dispatches
registry actions on the lh:kbd-<action> convention, but the sidebar's
listener sat on the pre-convention name "lh:toggle-sidebar" — a name
nothing ever dispatches, so ⌘B silently did nothing while its tooltip
and cheat-sheet row kept claiming the binding. A sweep of every lh:
listener confirmed the sidebar was the lone stray (chat-renamed and
graph-revision are deliberate non-kbd events).

Fix, structural: kbdEventForAction(action) exported from
src/core/keyboard.ts — the ONE spelling — and both sides compose
through it (dispatcher's default branch, sidebar's toggle listener);
keyboard-shortcuts re-exports the helper so the contract pin can assert
no second spelling exists. The mismatch is now impossible by
construction.

Thinking pill: label trimmed to "Thinking" with its real shortcut via
the registry-composition path — "Thinking (⇧⇥)" (cycle-thinking,
rebind-live like every Hint suffix).

Pins (tests/keyboard-toggle-sidebar.test.ts): the full chain — mod+b →
actionForBinding → toggle-sidebar → kbdEventForAction →
lh:kbd-toggle-sidebar; formatBinding("shift+tab") → ⇧⇥; the
dispatcher-imports-the-same-helper contract.

Live-verified on :3001: ⌘B visually toggles on home, /chat/[id], and
/chat/new (sidebar 0↔288px, hamburger slot 0↔36); with the rebind
lh:keymap {"toggle-sidebar":"mod+j"}: ⌘J toggles and ⌘B is inert
(rebind-live); thinking pill renders "Thinking (⇧⇥)"; keymap restored,
sidebar left open.

src/core/keyboard.ts

@@ -163,6 +163,18 @@ export function eventBinding(e: KeyboardEvent): string {
 	return [...mods, e.key.toLowerCase()].join("+");
 }
 
+/** The window event name a registry action dispatches/answers on —
+ *  the ONE spelling shared by the dispatcher (keyboard-shortcuts) and
+ *  every surface listener. Born from the ⌘B bug (owner interlude
+ *  2026-09-25): the sidebar listened on the pre-convention name
+ *  "lh:toggle-sidebar" while the dispatcher sent "lh:kbd-toggle-sidebar",
+ *  so ⌘B silently did nothing. With both sides composing through this
+ *  helper the mismatch is structurally impossible.
+ */
+export function kbdEventForAction(action: KeyAction): string {
+	return `lh:kbd-${action}`;
+}
+
 /** True when the event lands in a typing surface (input, textarea, or a
  *  contentEditable). In one, only mod/alt combos (and Tab, which types
  *  nothing) may fire — bare keys belong to the field (typing, caret). */