[Backend] Add GET /version endpoint exposing build SHA, build time, and contract IDs

[ogazboiz]

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Why this matters

Operators need to know which version of the backend is running in each environment when triaging incidents. There is currently no /version endpoint, so they fall back to grepping logs or shelling into the container. A read-only endpoint exposing git_sha, build_time, and node_version is trivial to ship and immediately useful for runbooks and the staging smoke test.

Acceptance criteria

• Add GET /version returning { gitSha, builtAt, nodeVersion, contracts: { loanManager, lendingPool, remittanceNft, multisigGovernance } }.
• Read GIT_SHA and BUILD_TIME from environment variables, falling back to "unknown".
• Wire those into the production backend/Dockerfile via ARG/ENV at build time.
• Add a Jest test covering the response shape.

Files to touch

• backend/src/app.ts
• backend/Dockerfile
• backend/src/__tests__/health.test.ts (or a new version.test.ts)
• .github/workflows/deploy-staging.yml (pass GIT_SHA/BUILD_TIME build args)

Out of scope

• Exposing the same on the frontend (/_status page is a separate issue).
• Surfacing it in a UI banner.

[MissBlue00]

@MissBlue00 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi can I be assigned to this issue?

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[Anuoluwapo25]

@Anuoluwapo25 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, Please can i work on this issues

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[drips-wave]

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