feat: implement bounty milestone approval

[zainabb-dev]

Overview

This PR implements the missing approve_bounty escrow interface for the Stellar Guilds contract. Fully funded bounties now enter a Funded state first, and an admin must explicitly approve a specific address before that address can claim the bounty. This replaces the old immediate first-come-first-served claim behavior for funded bounties.

Related Issue

Closes #109

Changes

⚙️ Bounty Approval Flow

• [MODIFY] contract/src/bounty/mod.rs

  • Added approve_bounty(env, bounty_id, approver, claimer) for admin-controlled bounty approval.
  • Enforced that a bounty must be in Funded state before approval.
  • Updated claim_bounty so only the approved address can claim after admin approval.
  • Changed fully funded bounties to transition into Funded instead of becoming immediately claimable.

• [MODIFY] contract/src/bounty/types.rs

  • Added the Funded bounty lifecycle state.
  • Extended BountyApprovedEvent to include the approved claimer address.

🧩 Contract Interface

• [MODIFY] contract/src/lib.rs
  • Exposed the new public approve_bounty contract method.
  • Updated bounty interface documentation to reflect the approval-before-claim flow.

✅ Test Coverage

• [MODIFY] contract/src/bounty/tests.rs

  • Added tests for successful admin approval.
  • Added tests to verify approval fails outside Funded state.
  • Added tests to verify claiming requires prior approval.
  • Added tests to verify only the approved address can claim.
  • Updated lifecycle, cancellation, escrow, and admin tests to match the new funded → approved → claimed flow.

• [MODIFY] contract/test_snapshots/...

  • Refreshed Soroban test snapshots impacted by the new bounty lifecycle and events.

Verification Results

Acceptance Criteria	Status
Admin can approve a bounty only when it is funded	✅
Approved claimer is the only address allowed to claim	✅
Existing bounty escrow lifecycle still works after approval step	✅
Targeted bounty contract tests pass	✅

How to Test

# 1. Confirm you're on the branch
git branch --show-current

# 2. Run the targeted bounty contract tests
cargo test bounty --manifest-path contract/Cargo.toml

# 3. Optional: inspect the changed files
git diff -- contract/src/lib.rs contract/src/bounty/mod.rs contract/src/bounty/types.rs contract/src/bounty/tests.rs

Screenshots

✅ Bounty contract tests pass

a screenshot of:

cargo test bounty --manifest-path contract/Cargo.toml

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[gabito1451]

please resolve conflicts , ensure your branch is also up to date and push again. nice implementation. thank you