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/rea/probe-todo12-open-appearance-dark.json

@@ -0,0 +1,13 @@
+{
+  "include_fonts": false,
+  "include_message_content": false,
+  "track_selectors": [
+    ".settings-navigation__item",
+    ".appearance-panel",
+    ".appearance-card"
+  ],
+  "actions": [
+    { "kind": "click", "step_id": "open-appearance-to-restore-light", "selector": ".settings-navigation__item", "index": 3, "frames": 0 },
+    { "kind": "wait", "step_id": "appearance-dark-ready-to-restore", "duration_ms": 400, "frames": 1 }
+  ]
+}