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/components/usage/StatCards.vue

@@ -41,7 +41,7 @@ function formatCost(n: number): string {
       <div class="stat-label">{{ t('usage.cacheHitRate') }}</div>
       <div class="stat-value">{{ usageStore.cacheHitRate !== null ? usageStore.cacheHitRate.toFixed(1) + '%' : '--' }}</div>
       <div class="stat-sub" v-if="usageStore.cacheHitRate !== null">
-        {{ formatTokens(usageStore.totalCacheTokens) }} tokens
+        {{ formatTokens(usageStore.totalCacheTokens) }} {{ t('usage.tokens') }}
       </div>
     </div>
   </div>