fix(a11y): the keyboard shortcuts dialog lists every shortcut (#334)

The ? dialog showed 7 shortcuts and left out Ctrl+K, ↑ to edit, all
composer formatting keys and the push-to-talk / deafen keys. Add them:
formatting rows are generated from the editor's INLINE_HOTKEYS /
BLOCK_HOTKEYS so they can't drift, and the call keys show the user's
own bindings.

Fixes #334

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/features/shortcuts/shortcutLabels.test.ts

@@ -0,0 +1,16 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { hotkeyKeys, keyCodeLabel } from './shortcutLabels';
+
+test('hotkeyKeys (#334)', () => {
+  assert.deepEqual(hotkeyKeys('mod+b', 'Ctrl'), ['Ctrl', 'B']);
+  assert.deepEqual(hotkeyKeys("mod+'", '⌘'), ['⌘', "'"]);
+  assert.deepEqual(hotkeyKeys('mod+[', 'Ctrl'), ['Ctrl', '[']);
+});
+
+test('keyCodeLabel (#334)', () => {
+  assert.equal(keyCodeLabel('KeyM'), 'M');
+  assert.equal(keyCodeLabel('Digit1'), '1');
+  assert.equal(keyCodeLabel('Space'), 'Space');
+  assert.equal(keyCodeLabel(''), 'Not set');
+});