feat(errors): add typed error subclasses for each error code (#327)

[bukeeastrey]

Description

Addresses #327 by introducing a dedicated typed error hierarchy rooted in GuildPassError, providing typed subclasses for every error code defined in errorCodes.ts.

Previously, consumers had to inspect error.code string/enum comparisons to distinguish error types. With these changes, consumers can use idiomatic TypeScript instanceof checks (e.g., if (e instanceof NetworkError) ...) while maintaining full backward compatibility with string-based checks.

Key Changes

• Base Class (GuildPassError): Extends JavaScript's built-in Error, properly sets the prototype chain for transpiled instanceof checks, and provides support for HTTP status codes, structured details, causes, and JSON serialization.
• Error Codes (errorCodes.ts): Defined standard error codes and transport codes (NETWORK_ERROR, TIMEOUT_ERROR, CIRCUIT_OPEN, UPSTREAM_ERROR, INVALID_CONFIG, ACCESS_DENIED, UNAUTHORIZED, FORBIDDEN, NOT_FOUND, VALIDATION_ERROR, RATE_LIMIT_EXCEEDED, CONFLICT, INTERNAL_ERROR, CONTRACT_ERROR, INVALID_SIGNATURE, BAD_REQUEST, UNSUPPORTED, and domain not-found codes).
• Typed Error Subclasses (errorTypes.ts):
  • NetworkError
  • TimeoutError
  • UpstreamError
  • CircuitOpenError
  • InvalidConfigError
  • AccessDeniedError
  • UnauthorizedError
  • ForbiddenError
  • NotFoundError
  • ValidationError
  • RateLimitError (RateLimitExceededError)
  • ConflictError
  • InternalError
  • ContractError
  • InvalidSignatureError
  • BadRequestError
  • UnsupportedError
  • MembershipNotFoundError, GuildNotFoundError, PassNotFoundError
• Re-exports & Mirroring:
  • Exported all error classes, codes, and types from @guildpass/integration-client.
  • Unified HTTP transport errors in packages/integration-client/src/http/errors.ts and circuitBreaker.ts.
  • Mirrored src/errors/ for consumer convenience.
  • Added test:run alias script to root package.json.

Testing

• Added unit test suite in packages/integration-client/test/errors.test.js and packages/integration-client/test/errors.test.ts.
• Verified instanceof Error, instanceof GuildPassError, and instanceof <Subclass> behavior.
• Verified backward compatibility of .code properties.
• Verified try ... catch pattern matching using instanceof.
• Ran pnpm typecheck across all workspace projects (passed with 0 errors).
• Ran pnpm --filter @guildpass/integration-client test (22/22 tests passing).

Closes #327