fix(bounties): prevent bounties from getting permanently stuck on escrow release failure

[windy202508]

Problem

Fixes #46

When markMergedAndRelease() was called, the bounty status was persisted to MERGED before attempting the escrow release. If the release failed (e.g., Soroban RPC timeout, network error), the bounty was permanently stuck because:

1. The state machine had no MERGED -> MERGED transition (no retry possible)
2. The only other exit was REFUNDED, which would return funds to the sponsor for completed work

Solution

1. Added RELEASE_PENDING status to BountyStatus enum

This represents a bounty whose PR has been merged and is awaiting successful escrow release.

2. Modified state machine transitions

MERGED -> RELEASE_PENDING
RELEASE_PENDING -> PAID (success)
RELEASE_PENDING -> RELEASE_PENDING (retry on failure)
RELEASE_PENDING -> REFUNDED (admin override)

3. Refactored markMergedAndRelease()

• First transition to MERGED and save (records the merge event)
• Then transition to RELEASE_PENDING before attempting escrow release
• On success: transition to PAID
• On failure: stay in RELEASE_PENDING (allows retry via repeated calls)
• Support retry: if called on a RELEASE_PENDING bounty, re-attempt the release

4. Updated dependent services

• ReputationService and AnalyticsService now include RELEASE_PENDING in their "completed work" checks

Testing

• ✅ Updated unit tests for state machine transitions
• ✅ Added test: escrow failure → RELEASE_PENDING recovery
• ✅ Added test: retry from RELEASE_PENDING → PAID
• ✅ Added test: unfunded bounty merges directly to PAID

Manual Testing

1. Create a bounty, fund it, claim it, mark in review
2. Call markMergedAndRelease() with escrow service configured to fail
3. Verify bounty status is RELEASE_PENDING (not stuck at MERGED)
4. Re-configure escrow service to succeed
5. Call markMergedAndRelease() again
6. Verify bounty status transitions to PAID

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