[codex] Honor runtime bulkMaxItems config

[pq198363-ops]

Summary

• Applies the runtime bulkMaxItems config to both usage and service bulk endpoints.
• Adds a guarded maximum of 1000 for bulkMaxItems so config changes cannot create unbounded in-memory batches.
• Documents the shared runtime bulk limit in the README.

Closes #90

RED / GREEN evidence

• RED before implementation: focused bulk-limit tests failed because usage bulk still accepted 3 items after lowering bulkMaxItems to 2, services bulk still rejected 51 items after raising the limit to 60, and config accepted bulkMaxItems: 1001.
• GREEN after implementation: the focused dist/bulk-limit.test.js test passed.

Verification

• npx prettier --check README.md src/store/state.ts src/routes/config.ts src/routes/usage.ts src/routes/services.ts src/bulk-limit.test.ts src/services.test.ts
• npm run lint
• npm run build
• $env:NODE_ENV='test'; node --test dist/*.test.js dist/**/*.test.js (92 tests, 11 suites, 92 pass, 0 fail)
• git diff --check