feat: add structured API request/response logging middleware

[1sraeliteX]

• Add sanitization utilities (lib/sanitize.ts) for redacting sensitive data
• Add structured JSON logging (lib/logger.ts) for all /api/* routes
• Add request ID generation and tracking (lib/requestId.ts)
• Add comprehensive test suite (tests/unit/sanitize.test.ts) with 31 tests
• Add complete documentation (docs/logging.md)
• Integrate logging into middleware.ts with request/response tracking
• Add LOG_LEVEL configuration to .env.example

Features:

• Never logs request bodies to prevent sensitive data exposure
• Automatically sanitizes response data before logging
• Redacts sensitive fields: password, token, apiKey, privateKey, etc.
• Partially masks: email (us***@), wallet addresses (GBXXXX)
• Configurable log levels: debug, info, warn, error
• Request ID tracking across logs via X-Request-ID header
• Recursion depth limit (5 levels) to prevent infinite loops
• Case-insensitive field matching for sensitive fields

All tests passing (31/31 sanitize tests + existing tests) TypeScript compilation: zero errors
Build: successful

[1sraeliteX]

@maintainer check and merge my PR!

[Baskarayelu]

link the issue