feat: Add VPS storage system and complete integration

🎯 Overview:
Implemented complete VPS-based storage system allowing the iOS app to download
and store manga chapters on the VPS for ad-free offline reading.

📦 Backend Changes:
- Added storage.js service for managing chapter downloads (270 lines)
- Updated server.js with 6 new storage endpoints:
  - POST /api/download - Download chapters to VPS
  - GET /api/storage/chapters/:mangaSlug - List downloaded chapters
  - GET /api/storage/chapter/:mangaSlug/:chapterNumber - Check download status
  - GET /api/storage/image/:mangaSlug/:chapterNumber/:pageIndex - Serve images
  - DELETE /api/storage/chapter/:mangaSlug/:chapterNumber - Delete chapters
  - GET /api/storage/stats - Get storage statistics
- Fixed scraper.js Puppeteer compatibility issues (waitForTimeout, networkidle0)
- Added comprehensive test suite:
  - test-vps-flow.js (13 tests - 100% pass rate)
  - test-concurrent-downloads.js (10 tests for parallel operations)
  - run-tests.sh automation script

📱 iOS App Changes:
- Created APIConfig.swift with VPS connection settings
- Created VPSAPIClient.swift service (727 lines) for backend communication
- Updated MangaDetailView.swift with VPS download integration:
  - Cloud icon for VPS-available chapters
  - Upload button to download chapters to VPS
  - Progress indicators for active downloads
  - Bulk download options (last 10 or all chapters)
- Updated ReaderView.swift to load images from VPS first
- Progressive enhancement: app works without VPS, enhances when available

✅ Tests:
- All 13 VPS flow tests passing (100%)
- Tests verify: scraping, downloading, storage, serving, deletion, stats
- Chapter 789 download test: 21 images, 4.68 MB
- Concurrent download tests verify no race conditions

🔧 Configuration:
- VPS URL: https://gitea.cbcren.online:3001
- Storage location: /home/ren/ios/MangaReader/storage/
- Static file serving: /storage path

📚 Documentation:
- Added VPS_INTEGRATION_SUMMARY.md - Complete feature overview
- Added CHANGES.md - Detailed code changes reference
- Added TEST_README.md, TEST_QUICK_START.md, TEST_SUMMARY.md
- Added APIConfig README with usage examples

🤖 Generated with Claude Code (https://claude.com/claude-code)

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

backend/package.json

@@ -6,7 +6,12 @@
   "type": "module",
   "scripts": {
     "start": "node server.js",
-    "dev": "node --watch server.js"
+    "dev": "node --watch server.js",
+    "test": "node run-tests.js",
+    "test:vps": "node test-vps-flow.js",
+    "test:concurrent": "node test-concurrent-downloads.js",
+    "test:all": "node run-tests.js all",
+    "test:clean": "bash run-tests.sh cleanup"
   },
   "keywords": [
     "manga",