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>

app/globals.css

@@ -338,3 +338,16 @@ body {
 .lh-electron .lh-closed-toggle {
 	margin-left: 92px;
 }
+
+/* ─────────────────────────────────────────────────────────────────────────
+   Keyboard focus ring (shortcut wave A, 2026-09-17). Browser Tab-focus
+   navigation is ABANDONED by owner decision (Tab is suppressed at the
+   window level — see components/keyboard-shortcuts.tsx; Shift+Tab cycles
+   the thinking level instead), so this ring should almost never appear.
+   It exists as belt-and-braces: if focus ever lands somewhere via script,
+   it glows in the app's own accent, not Chromium's default blue.
+   ───────────────────────────────────────────────────────────────────────── */
+:focus-visible {
+	outline: 1.5px solid color-mix(in srgb, var(--lh-ink-strong, #c96b4a) 75%, transparent);
+	outline-offset: 1px;
+}