feat(EM-45): Define REST API Standards and Migrate from Springfox to SpringDoc OpenAPI 3

[devin-ai-integration]

feat(EM-45): Add ftgo-api-standards library with SpringDoc OpenAPI 3 config

Summary

Creates the libs/ftgo-api-standards/ shared library to replace the monolith's Springfox-based common-swagger module with SpringDoc OpenAPI 3. Includes:

• Standard response DTOs: ApiResponse<T> (success/error envelope), ErrorResponse (with field-level errors), PageResponse<T> (pagination wrapper)
• SpringDoc auto-configuration: FtgoOpenApiAutoConfiguration that creates an OpenAPI bean with configurable info, Bearer JWT security scheme, and server definitions via FtgoApiProperties (ftgo.api.* prefix)
• Spring Boot 3.x auto-discovery via META-INF/spring/AutoConfiguration.imports
• Version catalog update: Added springdoc-openapi-starter-common library alias to gradle/libs.versions.toml
• REST API standards documentation in docs/api-standards/: naming conventions, versioning strategy (URL path-based), and error handling standards

The module is a standalone Gradle 8.7 project (matching sibling ftgo-common's pattern), with unit tests for all DTOs and the auto-configuration. Build passes with all tests green. No existing monolith source files or root settings.gradle were modified.

Review & Testing Checklist for Human

• Standalone module architecture: The module has its own Gradle wrapper (8.7) and settings.gradle, consistent with ftgo-common. Confirm this standalone structure works for your composite build / service consumption strategy — services will need to declare a dependency on this module somehow (composite build, local maven publish, etc.)
• Hardcoded dependency versions: build.gradle hardcodes springdoc 2.5.0, spring-boot 3.2.5, jackson 2.17.0 etc. rather than referencing the version catalog (standalone projects can't). Verify these match libs.versions.toml and accept the version-drift risk, or consider adding a comment/check
• No reusable GlobalExceptionHandler: The error-handling.md doc shows example @RestControllerAdvice code, but the library only provides the ErrorResponse DTO — each service must implement its own handler. Confirm this is the desired boundary
• Integration test gap: Unit tests verify auto-config bean creation, but don't test actual /swagger-ui or /v3/api-docs endpoint availability. Consider adding a @SpringBootTest integration test in a follow-up if needed
• Documentation alignment: Review docs/api-standards/*.md to ensure naming conventions, versioning strategy, and error codes match team standards

Notes

• All tests pass locally with Java 17
• Gradle wrapper binary (gradle-wrapper.jar) is included per standard Gradle project structure
• Link to Devin run: https://app.devin.ai/sessions/beee0739443140ba8e91be8dfe837ff2
• Requested by: @abj453demo

[devin-ai-integration]

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