Analyze and document code functionality

[Cretezy]

• Add validation for required environment variables (CLOUDFLARE_D1_ACCOUNT_ID, CLOUDFLARE_D1_DATABASE_ID, CLOUDFLARE_D1_API_KEY) with clear error messages
• Add optional onProgress callback parameter to createBackup function for progress logging
• Add detailed progress logging throughout backup process:
  • Table count and current table being processed
  • Row counts per table
  • Progress percentage for large tables (>1000 rows)
  • Indexes/triggers/views processing
  • Completion message
• CLI now logs progress to console by default
• Add package-lock.json from npm install