Pull Request Overview: Client Resilience, Quota Waiver Policy & Bilingual Localization

This pull request introduces connection resilience, client-side data handling utilities, an automatic quota exemption policy for connection/provider failures, and complete English/Vietnamese bilingual localization across the platform.

Frontend Changes (data-crawler-fe)

1. Real-Time SSE Resilience & Connection Recovery

• Exponential Backoff Algorithm (use-event-source.ts):
  • Implemented progressive retry intervals: 1s → 2s → 4s → 8s → 16s → max 30s.
  • Added event listeners for online and tab visibilitychange to trigger immediate reconnects when connectivity returns.
• Visual SSE Status Badge (sse-status-badge.tsx):
  • Emerald (Live): Real-time active stream with ping animation.
  • Amber (Reconnecting): Spinner with countdown timer (Reconnecting (2s)...).
  • Rose (Disconnected): Alert state with an interactive "Retry" button.

2. Network State Detection

• Offline Banner (network-status-banner.tsx):
  • Sticky earth-orange notification informing users when the browser loses Internet connection.
• React 19 Compliant Hook (use-network-status.ts):
  • Complies with React 19 rules (initializes via lazy state function to avoid cascading re-renders).

3. Desktop Web Notifications

• Web Notification Utility (web-notifications.ts):
  • Alerts users upon job completion only when the tab is backgrounded (document.hidden === true).
• Interactive Toggle Button (notification-toggle-button.tsx):
  • Provides permission requesting, visual state indicators, and feedback toasts.

4. Client Data Handling Utilities

• JSON Syntax Highlighter (json-viewer.tsx):
  • High-performance tokenized syntax coloring, compact/formatted view toggle, search query filter, and line number gutter.
• Reusable Copy Button (copy-button.tsx):
  • Smooth 2-second checkmark transition with optional toast notifications.
• File Downloader Helper (download-helper.ts):
  • Standardized filename generation and automatic URL.revokeObjectURL() memory cleanup.

5. Full Bilingual Localization (English & Vietnamese)

• Central Dictionary (translations.ts):
  • Added 100% matching translation keys across vi and en for: network, sse, notifications, jsonViewer, copyAction, crawlErrors, quota, and jobDetail.
  • Aligned semantic labels (Nguyên nhân: <-> Reason:).
• Crawl Error Localization Helper (crawl-error-helper.ts):
  • Translates technical raw errors (HTTP 402, Timeouts, Refused, DNS) into user-friendly explanations according to the active locale.
• UI Deduplication (crawl-jobs/[id]/page.tsx):
  • Removed duplicate badges and streamlined root cause presentation to a single, concise informational box.