feat: finalize backend contribution scope

[anupam7984]

Summary

This PR completes the assigned backend contribution scope in one branch:

• Adds/validates Soroban RPC health integration in backend health surfaces (/health and /health/rpc) and keeps status visible in responses.
• Documents contract upgradeability approach and rollout strategy, including a new Future: upgradeability section in docs.
• Ensures campaign creation flow is covered for legacy compatibility by validating POST /api/campaigns behavior in tests.
• Strengthens backend CI with GitHub Actions for pull requests and pushes to main, using Node 20 and backend checks.

Changes Included

1) Health + Soroban RPC status

• Health endpoints include Soroban RPC status details.
• /health/rpc returns degraded/failure status with 503 when RPC checks fail.
• Test coverage verifies reachable and failing RPC scenarios.

2) Campaign create endpoint behavior

• Legacy route compatibility is validated for:
  • POST /api/campaigns
• Test confirms:
  • 201 Created
  • response includes created campaign payload (name, description, rewardPerAction, etc.)

3) Upgradeability documentation

• Expanded upgradeability guidance with migration-first operational steps.
• Added short Future: upgradeability sections to:
  • docs/upgradeability.md
  • docs/ARCHITECTURE_OVERVIEW.md
• Covers deployer/governance-oriented upgrade path, migration checkpoints, and rollback readiness.

4) Backend CI workflow

• Updated/added backend workflow under .github/workflows/backend-ci.yml:
  • triggers on:
    • pull requests to main
    • pushes to main
  • uses Node 20
  • installs with npm ci
  • runs backend tests
  • runs lint/typecheck conditionally when scripts exist

Files Changed

• .github/workflows/backend-ci.yml
• backend/src/index.test.js
• docs/upgradeability.md
• docs/ARCHITECTURE_OVERVIEW.md

Test Plan

• Run backend tests locally:
  • npm run test --workspace=backend
• Confirm all tests pass
• Verify CI workflow targets PR + push to main
• Verify docs render correctly in markdown preview

Backward Compatibility

• Legacy API route behavior remains supported and now has explicit test coverage for campaign creation.
• No breaking API contract changes introduced in this PR.

Notes

This PR focuses on contribution safety and maintainability: observable health checks, tested campaign behavior, CI guardrails, and clear future upgradeability guidance.

closes #108
closes #98
closes #100
closes #136

[vercel]

Someone is attempting to deploy a commit to the joelpeace48-cell's projects Team on Vercel.

A member of the Team first needs to authorize it.

[drips-wave]

@anupam7984 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits