Add input validation to Employee REST API

[devin-ai-integration]

Summary

Adds Bean Validation constraints to the Employee REST API so that invalid input is rejected with a 422 response before reaching the database.

Changes:

• Employee entity: Added @NotBlank and @Size(min=1, max=255) annotations to firstName, lastName, and jobTitle fields. This rejects null, empty, and whitespace-only values, and enforces a 255-character max length.
• EmployeeResource: Added @Valid on the createEmployee method parameter so Dropwizard triggers validation automatically and returns structured error responses on constraint violations.
• pom.xml: Added jaxb-api and jaxb-runtime as test-scoped dependencies for Java 11 compatibility.
• EmployeeValidationTest: 11 new test cases covering valid input, null/empty/blank values for each field, all-null input, max-length boundary, and over-max-length rejection.

Review & Testing Checklist for Human

• Verify 422 responses are returned when POSTing invalid Employee JSON (null, empty, or blank fields; fields exceeding 255 chars)
• Confirm valid Employee creation still works as expected via POST /employee
• Review that @NotBlank from org.hibernate.validator.constraints is appropriate for the Dropwizard 1.0.5 / Hibernate Validator 5.x version in use

Notes

• Dropwizard's built-in ConstraintViolationExceptionMapper handles the error response formatting automatically — no custom exception mapper was needed.
• The @NotBlank annotation covers both null and whitespace-only checks, while @Size adds the upper bound constraint.

Link to Devin session: https://app.devin.ai/sessions/29e94bdec4d9451283bc8fb83f12be2e
Requested by: @WesternConcrete

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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End-to-End Test Results

Tested input validation on POST /employee by running the server locally and issuing curl requests against it. All 6 tests passed.

Validation Tests (6/6 passed)

#	Test	Expected	Actual	Result
1	Valid employee creation	HTTP 200 + employee JSON	200 — {"id":2,"firstName":"Alice","lastName":"Smith","jobTitle":"Senior Dev"}	PASSED
2	Missing firstName	HTTP 422 + error referencing firstName	422 — {"errors":["firstName may not be empty"]}	PASSED
3	Whitespace-only jobTitle (" ")	HTTP 422 (proves @NotBlank not just @NotNull)	422 — {"errors":["jobTitle may not be empty"]}	PASSED
4	256-char firstName	HTTP 422 (proves @Size(max=255))	422 — {"errors":["firstName size must be between 1 and 255"]}	PASSED
5	Empty {} body	HTTP 422 with 3 errors (one per field)	422 — 3 errors for firstName, lastName, jobTitle	PASSED
6	Invalid data NOT persisted	GET /employee returns only valid records	Only 2 valid records returned, no invalid data	PASSED

No escalations. Devin session