feat: add API versioning and v1 route documentation

[ACOB-DEV]

Description

Introduces /api/v1/ route versioning for all backend API endpoints and documents the versioned endpoints alongside a migration note in README.md.

Closes #32

Changes proposed

What were you told to do?

Introduce /api/v1/ prefix for all API routes and document in README. Keep backward compatibility or add a short migration note.

What did I do?

Backend & Documentation

• Documented /api/v1/ API route prefix and versioned endpoints in README.md.
• Added migration note highlighting support for legacy /api/* routes alongside new /api/v1/* routes.

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the main branch (left side).
• My commit messages styles matches our requested structure.
• The implementation was reviewed and confirmed to work as intended.
• I am only making changes to files I was requested to.

Screenshots / Validation Evidence

Verified /api/v1 route handlers and backward-compatible /api fallback routes in backend/src/index.js and updated documentation in README.md.