feat: add deploy_health handler with DB, Redis caching, and tests

[malik203]

feat: add deploy health handler

Adds GET/POST/PATCH endpoints for tracking contract deployment health, backed by PostgreSQL
and Redis.

Changes

• migrations/20260527000000_deployments.sql — new deployments table (contract_id, version,
  status, error_message, metadata, timestamps)

• src/api/handlers/deploy_health.rs — four handlers:

  • POST /api/v1/deployments — register a deployment (starts as pending)
  • GET /api/v1/deployments/:id — fetch by UUID (Redis-cached, 30s TTL)
  • GET /api/v1/deployments/contract/:contract_id — list all deployments for a contract
    (cached)
  • PATCH /api/v1/deployments/:id/status — update health status (pending | healthy | degraded
    | failed), invalidates cache

• src/api/handlers/mod.rs — registers the new module

• README.md — documents the new endpoints

Testing

13 unit tests covering status parsing, serde roundtrips, request deserialization, and input
validation. No external services required to run the unit tests.
closes #181

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