Title: SZ-7 – Document REST endpoints with Springdoc

We need to annotate the main REST controllers with Springdoc OpenAPI annotations so that Swagger UI shows meaningful documentation for internal and external devs.

Applies to:

• GET /users (filters: username, email, role)
• GET /projects (filters: ownerId, startAfter, endBefore)
• GET /issues (filters: status, priority, severity, assigneeId, projectId)

Tasks:

• Add springdoc-openapi-starter-webmvc-ui to pom.xml
• Annotate each controller method with @Operation and @Parameter
• Use @Parameter(hidden = true) for Pageable
• Ensure enums like IssueStatus, IssuePriority, etc., show up cleanly
• Use @DateTimeFormat for LocalDate parameters
• Optionally group endpoints with @Tag

Estimate (rough):

• Springdoc dependency + config: 0.5h
• Annotate UserController: 0.5h
• Annotate ProjectController: 0.5h
• Annotate IssueController: 0.5h
• Swagger UI review + testing: 0.5h
• Enum/date formatting: 0.5–1.0h

Total: 2.5 to 3.5 hours

This is split out from SZ-2 to keep the logic and documentation efforts separate.