fix: validate workout exercise inputs

[NAND-369]

Summary

Closes #35

• Add frontend validation for exercise reps, sets, and weight
• Prevent negative reps, sets, and weight
• Prevent decimal values for reps and sets
• Allow decimal values for weight
• Reject NaN, Infinity, and non-numeric values
• Add backend validation before workout state persistence
• Return HTTP 400 for invalid workout data
• Add frontend and backend regression tests

Implementation

Frontend

• Added validation.js
• Added validation guards to Workout.jsx
• Improved NumberField and Stepper
• Added validation regression tests

Backend

• Added api/validation.js
• Added validation to PUT /api/data
• Invalid workout state is rejected before atomicWrite()
• Added backend regression tests
• Added npm test script

Verification

• Frontend: 219 tests passed
• Backend: 21 tests passed
• git diff --check: clean

[SunriseDuarte]

Heads up: openGym has moved to GitLab.
-> GitLab

The GitHub repo is no longer maintained (the account was suspended, so it's out of my hands). Please re-open this issue/PR on GitLab so it doesn't get lost, I'll pick it up there. Questions, help and roadmap discussion now happen in Discord:
-> Discord

Sorry for the noise, and thanks for sticking around.
more infos here: openGym

[NAND-369]

Thanks for the heads-up! I’ve moved the contribution to GitLab and reopened Issue #35 there.

New MR: https://gitlab.com/DuarteSantos8/opengym/-/merge_requests/33

The validation changes have been ported to the current GitLab main branch, and the GitLab CI pipeline is passing. Thanks for maintaining the project!