Add unit tests for HealthController, IpfsService, GistCleanupService and live Soroban paths

[demilade18-git]

Closes #1413
Closes #1414
Closes #1415
Closes #1416

• health.controller.spec.ts: both checks pass, database fails, PostGIS fails, both fail, and the error message is surfaced
• ipfs.service.spec.ts: dev-mode pinJson (mock CID) and getJson, live pinJson with a mocked Pinata client, retry-then-succeed, retry-then-fail, and getJson against the configured gateway (success and error status)
• soroban.service.live.spec.ts: mocked RPC server covering the success path and one failure path for postGist, getGist, isActive, listGistsByCell, getAdmin, reportGist and getEventsSince, including GistContractError mapping from a contract Err result
• gist-cleanup.service.spec.ts: handleExpiredGists() calls deleteExpired, logs only when the count is above zero, and a repository error propagates (the method does not catch; the test pins that behaviour)

Tests were written but not run (no dependencies installed).

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