feat: add simplified Space API and unit test infrastructure

[jimmieme]

Summary

• Add simplified one-step space registration API (POST /v2/platform/spaces)
• Add test mock implementations for Redis-dependent services
• Add comprehensive unit tests for API endpoints
• Update README with contributing guidelines

Changes

New Simplified API

• SpaceResource.java: New REST endpoint for simplified space registration
• SpaceRegistryInfo.java: Request DTO for space registration
• SpaceRegistryResult.java: Response DTO with network credentials
• RegistryService.registerSpace(): One-step registration combining box, user, and
  client registration

Test Infrastructure

• MockGTRClient.java: In-memory mock for Redis GT route client
• MockNSRClient.java: In-memory mock for Redis network server route client
• MockDistributedLockFactory.java: Mock for distributed locks (Redis mocked, MySQL
  real)

Unit Tests

• SpaceResourceTest.java: Tests for simplified space API
• NetworkResourceTest.java: Tests for network authentication API
• BasicResourceTest.java: Tests for status and ability endpoints

API Example

curl -X POST https://platform.example.com/v2/platform/spaces \
  -H "Content-Type: application/json" \
  -H "Request-Id: $(uuidgen)" \
  -d '{
    "boxUUID": "your-box-uuid",
    "userId": "admin",
    "clientUUID": "your-client-uuid",
    "subdomain": "myspace"
  }'

Test Plan

- All 39 unit tests pass
- MockGTRClient properly replaces Redis in tests
- MockNSRClient properly replaces Redis in tests
- MySQL locks work correctly in tests
- Network authentication returns correct credentials

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