Add E2E test that walks the full prediction lifecycle on a testnet contract

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox campaign. Author a Jest+supertest E2E that creates a market, places a prediction, resolves, claims, all on testnet.

Requirements and Context

• Uses testnet contract
• Cleans up after
• Runs nightly in CI
• Doc explains
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b task/e2e-lifecycle

2. Implement changes
   • tests/e2e/predictionLifecycle.test.ts (new)
   • .github/workflows/e2e.yml (new)
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

test: prediction lifecycle E2E

Acceptance Criteria

• Runs against testnet
• CI nightly
• Cleanup
• Doc shipped

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours