Fix bounty payment retry status flow

[cybercraftsolutionsllc]

Fixes #1901

Summary

• keep UpdateBountyPaymentStatus read-only for non-COMPLETE retry results
• return the V2 bot status (PENDING or FAILED) instead of falling through to NOTPAID
• add payment retry coverage for pending, failed, and completed status handling
• add the missing generated GetBountyByUnlockCode database mock so handler tests compile against the current interface

Validation

• go test ./handlers -run '^$' -count=1
• git diff --check

go test ./handlers -run TestUpdateBountyPaymentStatus -count=1 is blocked locally because the Postgres test DB is not running at localhost:5532, and Docker Desktop's daemon is unavailable for docker compose -f docker/testdb-docker-compose.yml -p test_db up -d.