feat(settings): replicate the WorkBuddy keyboard shortcuts panel and wire global bindings (TODO 12)

Recover the WorkBuddy 5.8.3 快捷键 page from REA evidence (keyboard-shortcuts-DOrivHwf.css + tokens): 49 recovered module rules, scoped light/dark tokens, the 24-row 命令/按键绑定/操作 sheet (panel 638x620, header 39, scroll 638x533, rows 41/45/44, keycaps 22) and the recording/ESC-cancel interaction.

Wire the panel into SettingsDialog and keep only real bindings honest: 14 of 24 rows are marked supported, the remaining rows stay visually 1:1 but are labelled 尚未接入 and cannot pretend to save custom keys. Add Ctrl+K search focus, Ctrl+B / Ctrl+Shift+B left/right sidebar toggles, Ctrl+N new conversation (App -> Sidebar path) and Esc-to-stop while generating; fix the sidebar search focus race introduced by conditional mounting.

Verify with scripts/verify-shortcuts-settings.cjs: 32 assertions covering geometry, row/key order, search filtering, recording/cancel, supported ids, dark theme surfaces and the four new global shortcuts in a real main window. All existing regressions stay green.

scripts/verify-settings-nav.cjs

@@ -125,10 +125,10 @@ if (!process.versions.electron) {
     // 原版 4 组；about 组按组件约定渲染为分隔线而不是标题。
     check('nav keeps the four recovered groups', [nav.groups.length, nav.dividers], [3, 1])
     // 通用(settings) 在 TODO 10 接入后同样可用。
-    const expectedDisabled = EXPECTED_TABS.filter(tab => !['settings', 'models', 'appearance'].includes(tab))
+    const expectedDisabled = EXPECTED_TABS.filter(tab => !['settings', 'models', 'appearance', 'keyboardShortcuts'].includes(tab))
     check('unwired entries stay disabled', nav.tabs.filter((tab, index) => nav.disabled[index] === 'true'), expectedDisabled)
     check('unwired entries keep the 暂未接入 hint', nav.titles.filter(title => (title ?? '').includes('暂未接入')).length, expectedDisabled.length)
-    check('settings, models and appearance stay enabled', nav.tabs.filter((tab, index) => !nav.disabled[index]), ['settings', 'appearance', 'models'])
+    check('settings, appearance, keyboard shortcuts and models stay enabled', nav.tabs.filter((tab, index) => !nav.disabled[index]), ['settings', 'appearance', 'keyboardShortcuts', 'models'])
 
     await step('settings-search-excludes-removed')
     await read(`(()=>{const input=document.querySelector('.settings-navigation input[type="search"]');