feat: add global keyboard shortcuts for timer toggle and show app

Register CmdOrCtrl+Shift+T (toggle timer) and CmdOrCtrl+Shift+Z
(show app) via tauri-plugin-global-shortcut. Shortcut keys are
configurable in Settings Timer tab. Shortcuts re-register on change.

src/App.vue

@@ -4,9 +4,37 @@ import TitleBar from './components/TitleBar.vue'
 import NavRail from './components/NavRail.vue'
 import ToastNotification from './components/ToastNotification.vue'
 import { useSettingsStore } from './stores/settings'
+import { useTimerStore } from './stores/timer'
 
 const settingsStore = useSettingsStore()
 
+async function registerShortcuts() {
+  try {
+    const { unregisterAll, register } = await import('@tauri-apps/plugin-global-shortcut')
+    await unregisterAll()
+    const toggleKey = settingsStore.settings.shortcut_toggle_timer || 'CmdOrCtrl+Shift+T'
+    const showKey = settingsStore.settings.shortcut_show_app || 'CmdOrCtrl+Shift+Z'
+
+    await register(toggleKey, () => {
+      const timerStore = useTimerStore()
+      if (timerStore.isStopped) {
+        if (timerStore.selectedProjectId) timerStore.start()
+      } else {
+        timerStore.stop()
+      }
+    })
+
+    await register(showKey, async () => {
+      const { getCurrentWindow } = await import('@tauri-apps/api/window')
+      const win = getCurrentWindow()
+      await win.show()
+      await win.setFocus()
+    })
+  } catch (e) {
+    console.error('Failed to register shortcuts:', e)
+  }
+}
+
 function applyTheme() {
   const el = document.documentElement
   const mode = settingsStore.settings.theme_mode || 'dark'
@@ -29,6 +57,7 @@ onMounted(async () => {
     (app.style as any).zoom = `${zoom}%`
   }
   applyTheme()
+  registerShortcuts()
 
   window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
     if (settingsStore.settings.theme_mode === 'system') applyTheme()
@@ -38,6 +67,10 @@ onMounted(async () => {
 watch(() => [settingsStore.settings.theme_mode, settingsStore.settings.accent_color], () => {
   applyTheme()
 })
+
+watch(() => [settingsStore.settings.shortcut_toggle_timer, settingsStore.settings.shortcut_show_app], () => {
+  registerShortcuts()
+})
 </script>
 
 <template>