feat: add web terminal, improve README, fix node-pty and i18n issues

- Add web terminal view with xterm.js and node-pty WebSocket backend
- Rewrite README with badges, feature table, mobile demo video
- Add package keywords and improved description for npm/GitHub SEO
- Fix node-pty spawn-helper missing execute permission after npm install -g
- Auto-fix node-pty permissions on CLI startup
- Fix duplicate 'error' key in en.ts and zh.ts i18n files
- Remove nested NSpin in PlatformSettings (causes invisible loading spinner)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/views/ChannelsView.vue

@@ -20,7 +20,7 @@ onMounted(() => {
     </header>
 
     <div class="channels-content">
-      <NSpin :show="settingsStore.loading">
+      <NSpin :show="settingsStore.loading || settingsStore.saving" size="large" :description="t('common.loading')">
         <PlatformSettings />
       </NSpin>
     </div>
@@ -40,5 +40,6 @@ onMounted(() => {
   flex: 1;
   overflow-y: auto;
   padding: 20px;
+  position: relative;
 }
 </style>