[Phase 5E] Docs finalization — api-contract update, error codes doc, README polish

[XpnsiveSharks]

Overview

Finalize all project documentation to reflect the complete implemented system. Update api-contract.md with missing endpoints, create the error codes reference, and polish README.md for handoff or presentation readiness.

Tasks

• Update docs/api-contract.md — add PATCH /api/tickets/{id}/confirm-resolved endpoint entry under Tickets section
• Create docs/error-codes.md — list all errorCode values, HTTP status, and description (output of Phase 5B)
• Review and update docs/data-models.md — confirm all entities match final DB schema (TicketAttachment, TicketResponse, Notification fields)
• Review and update docs/architecture.md — confirm package structure matches current src layout
• README.md — add Deployment section (output of Phase 5D), update Postman section to reference UCMS-Full collection, verify all doc links are valid
• Verify CONTRIBUTING.md issue template and PR template are up to date with current labels and checklist

Acceptance Criteria

• docs/api-contract.md includes all implemented endpoints including confirm-resolved
• docs/error-codes.md exists with all errorCode values documented
• docs/data-models.md matches final DB schema
• README.md has a working Deployment section and correct Postman reference
• All internal doc links resolve correctly
• No placeholder or TODO text remains in any doc file

References

• docs/api-contract.md
• docs/data-models.md
• docs/architecture.md
• docs/error-codes.md (to be created)
• README.md
• CONTRIBUTING.md