refactor(metadata): change boolean fields to Boolean type for improved null handling

[balazs-szucs]

📝 Description

Avoids:

2026-02-12T21:53:20.063-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] o.s.web.servlet.DispatcherServlet        : POST "/api/v1/tasks/start", parameters={}
2026-02-12T21:53:20.063-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped to org.booklore.controller.TaskController#startTask(TaskCreateRequest)
2026-02-12T21:53:20.065-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] o.s.web.method.HandlerMethod             : Could not resolve parameter [0] in public org.springframework.http.ResponseEntity<org.booklore.model.dto.response.TaskCreateResponse> org.booklore.controller.TaskController.startTask(org.booklore.model.dto.request.TaskCreateRequest): JSON parse error: Cannot map `null` into type `boolean` (set DeserializationConfig.DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES to 'false' to allow)
2026-02-12T21:53:20.066-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] .m.m.a.ExceptionHandlerExceptionResolver : Using @ExceptionHandler org.booklore.exception.GlobalExceptionHandler#handleHttpMessageNotReadableException(HttpMessageNotReadableException)
2026-02-12T21:53:20.067-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] o.s.w.s.m.m.a.HttpEntityMethodProcessor  : Using 'application/json', given [application/json, text/plain, */*] and supported [application/json, application/*+json, application/yaml]
2026-02-12T21:53:20.067-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] o.s.w.s.m.m.a.HttpEntityMethodProcessor  : Writing [org.booklore.exception.ErrorResponse@2c45186f]
2026-02-12T21:53:20.068-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] .m.m.a.ExceptionHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot map `null` into type `boolean` (set DeserializationConfig.DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES to 'false' to allow)]
2026-02-12T21:53:20.069-06:00 DEBUG 1 --- [booklore-api] [at-handler-2474] o.s.web.servlet.DispatcherServlet        : Completed 400 BAD_REQUEST

Errors

🏷️ Type of Change

• Bug fix
• New feature
• Enhancement to existing feature
• Refactor (no behavior change)
• Breaking change (existing functionality affected)
• Documentation update

🔧 Changes

🧪 Testing

📸 Screenshots / Video (MANDATORY)

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✅ Pre-Submission Checklist

All boxes must be checked before requesting review. Incomplete PRs will be closed without review. No exceptions.

• Code follows project style guidelines and conventions
• Branch is up to date with develop (merge conflicts resolved)
• Automated tests added or updated to cover changes (backend and frontend)
• All tests pass locally (./gradlew test for backend, ng test for frontend)
• Changes manually verified in local dev environment (including related features)
• Screenshots or video proving the change works are attached above (MANDATORY)
• Flyway migration versioning is correct (if schema was modified)
• Documentation PR submitted to booklore-docs (if user-facing changes)
• PR is reasonably scoped (PRs over 1000+ changed lines will be closed, split into smaller PRs)

🤖 AI-Assisted Contributions

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• Every line has been read, understood, and can be explained by the author
• PR is scoped to a single logical change, not a dump of everything the AI suggested
• Tests validate actual behavior, not just coverage (AI-generated tests often assert nothing meaningful)
• No dead code, placeholder comments, TODOs, or unused scaffolding

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💬 Additional Context (optional)