fix(auth): RegisterView fidelity port from design zip

Port A-group deltas from design zip (excluding bonus/pricing which
are explicitly out of scope):
- Narrative: N (not 5) 个订阅; add '// 5 分钟开始用' n-kicker;
  SVG hexagon logo (was emoji); n-bottom live status bar
- Add 3-step onboarding panel (创建账户 → 绑定订阅 → 生成 key)
  in narrative, active-step highlighted
- Add password strength meter (4 bars + text label 弱/中/强/极强)
- Add confirm-password field with live // matched/mismatch hint
- Add Terms & Privacy consent checkbox (submit gated)
- New i18n keys: confirmPasswordLabel/Placeholder, passwordsDoNotMatch

All existing Vue logic preserved (OAuth/Turnstile/verify code/
invitation+promo codes).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/i18n/locales/zh.ts

@@ -504,6 +504,7 @@ export default {
     puroLoginSub: '用你的 PURO AI 账户继续',
     puroRegisterTitle: '创建账户',
     puroRegisterSub: '5 分钟开始用 PURO AI',
+    confirmPasswordLabel: '确认密码',
   },
 
   // Dashboard