Implement Escrow-Based Reward Distribution

[Abd-Standard]

Description

Currently, rewards are transferred directly after task completion. Introduce an escrow mechanism where rewards are locked when a bounty is created and can only be released after successful task verification.

Requirements
Lock reward funds during bounty creation.
Release rewards only after approval.
Allow refunds if a bounty expires or is cancelled.
Emit events for deposits, releases, and refunds.
Handle failed transactions safely.

Acceptance Criteria
Funds remain locked until approval.
Approved contributors receive rewards automatically.
Refunds work correctly.
Unit tests cover all scenarios.

[Promise278]

i have experience with system design and archecture i would love to work on these please

[Bamzy123]

I have experience in handling issues like this and I'll submit PR within 2 days max.

[N-thnI]

Dear maintainer
Please assign me this issue

[grantfox-oss]

🦊 GrantFox — @N-thnI has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #130)
2. Your PR will be reviewed by the Core-Foundry maintainers

Good luck! Track your progress on GrantFox.