feat: implement milestone verification workflow

[xJeffx23]

Summary

• Add MilestoneSubmission, MilestoneReview, MilestoneVerificationHistory models + Prisma migration
• Full state machine: DRAFT → SUBMITTED → UNDER_REVIEW → APPROVED / REJECTED / REVISION_REQUESTED
• All org and admin/verifier endpoints with access control
• Notifications (email + WebSocket) on all state transitions
• 43 unit and integration tests passing
• New endpoints documented in docs/API.md

Test plan

-Run `npx jest --testPathPattern=milestone` — debe mostrar 43 tests passing
-Aplicar migración con `npx prisma migrate deploy` en staging

Closes #75

[BarryArinze]

Resolve conflict

[xJeffx23]

Ready @BarryArinze 🫡

[xJeffx23]

Ready conflicts 🫡 @BarryArinze

[BarryArinze]

I cant still merge due to conflicts

[xJeffx23]

I've resolved the conflicts again. 🚀

[xJeffx23]

@BarryArinze

[GBOYEE]

I'd like to work on this issue. I have background in devops and will submit a PR ASAP.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll add the CI config and test it locally before pushing
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll add the CI config and test it locally before pushing
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.