ci: enforce backend types and contract formatting

[kingeligma]

Summary

Resolves the four assigned issues with focused CI, cache, OpenAPI, and Rust contract changes.

Changes

• TypeScript type-checking is not enforced in CI despite build:tsc in package.json #1381: backend governance now runs npm run prisma:generate and npm run build; backend/package-lock is synchronized so npm ci succeeds.
• triggerCacheInvalidation crashes when a registered hook returns a non-array #1379: cache invalidation accepts the existing async vault hook and skips malformed non-array results without throwing; regression coverage added.
• OpenAPI spec must reflect the indexer check in the health response schema #1323: added a reusable HealthResponse OpenAPI schema with all dependency checks, including checks.indexer, wired /health to it, regenerated backend/openapi.json, and added a contract assertion.
• CI must enforce cargo fmt on Rust contracts before merge #1331: explicitly installs rustfmt in Rust CI, repairs malformed contract syntax/formatting, and updates Cargo.lock so locked workspace commands resolve the existing contract package.

Validation

Passed:

• npm ci --ignore-scripts --no-audit --no-fund in backend
• npm run lint in backend (0 errors)
• focused backend Jest tests: 5 passed
• npm run generate:openapi
• cargo fmt --all -- --check

Known baseline blockers documented for follow-up:

• npm run build currently reports 92 pre-existing TypeScript errors across Prisma model drift, logger APIs, telemetry, and unrelated modules.
• cargo test --workspace --locked reaches pre-existing Soroban contract compile errors, including missing VaultError, an overlong contract function name, and invalid BridgeError conversion signatures.

No CI failure is hidden or made non-blocking; #1381 intentionally adds the TypeScript build gate so these existing errors become visible to maintainers.

Fixes #1381
Fixes #1379
Fixes #1323
Fixes #1331

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