[Feature]: andidate onboarding — candidate must accept terms before campaign start

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Issue Description ✍️

Add a candidate approval flow: after a candidate is created, send them a verification link (off-chain), they accept, then the owner flips campaignActive = true. Frontend must show a “Pending acceptance” state.

Why: Prevents fake campaigns and ensures candidate consent.

### Record

- [x] I have synced all my node versions as mentioned in the project
- [x] I am using the same version of npm as is the project
- [x] My current branch is in sync with the development branch
- [x] I want to work on this issue