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/question-dock.tsx

@@ -443,9 +443,12 @@ function QuestionDockForm({
 							value={text}
 							onChange={(e) => setText(e.target.value)}
 							onKeyDown={(e) => {
-								// Esc ends dictation (the dictate decisions: click-again or Esc).
+								// Esc ends dictation (the dictate decisions: click-again
+								// or Esc) — stopPropagation claims it (keyboard wave
+								// A) so the window chain doesn't also abort a turn.
 								if (e.key === "Escape" && onEscape) {
 									e.preventDefault();
+									e.stopPropagation();
 									onEscape();
 									return;
 								}
@@ -465,9 +468,12 @@ function QuestionDockForm({
 							value={thinking}
 							onChange={(e) => setThinking(e.target.value)}
 							onKeyDown={(e) => {
-								// Esc ends dictation (the dictate decisions: click-again or Esc).
+								// Esc ends dictation (the dictate decisions: click-again
+								// or Esc) — stopPropagation claims it (keyboard wave
+								// A) so the window chain doesn't also abort a turn.
 								if (e.key === "Escape" && onEscape) {
 									e.preventDefault();
+									e.stopPropagation();
 									onEscape();
 									return;
 								}