feat(api,web): add fleet metadata to GET /api/health

[rvegajr]

Summary

Extends the lightweight GET /api/health endpoints on API and web with fleet build metadata (ok, service, commit, env, utc) per the cloud-agents health contract. Existing fields and HTTP 200 behavior are unchanged; /api/health/version is untouched.

Changes

• API (packages/api/src/routes/health/health.ts): adds fleet fields alongside existing status and timestamp.
• Web (packages/web/app/api/health/route.ts): adds fleet fields alongside existing status.
• Tests for commit from RAILWAY_GIT_COMMIT_SHA and "unknown" when unset.

Verified

corepack enable && pnpm install --frozen-lockfile
pnpm --filter @scholaracle/contracts build
pnpm build   # required in this VM before full type-check (workspace packages)
pnpm type-check
pnpm lint:strict
pnpm format:check
pnpm --filter @scholaracle/api test
pnpm --filter @scholaracle/web test

All commands exited 0.

Not changed

• /api/health/version, auth, CORS, CI, README, CHANGELOG (none in repo).