[codex] Configure server timeouts

[pq198363-ops]

Closes #95

Summary

• Configure HTTP request, headers, keep-alive, and inactive socket timeouts on the Node server.
• Add positive-integer environment overrides with safe fallback defaults.
• Document timeout controls and the header/keep-alive invariant.

Threat model

Slow or incomplete clients should not be able to hold request or socket resources indefinitely. Invalid, zero, negative, or decimal environment overrides fall back to safe defaults rather than disabling protection.

RED/GREEN evidence

• RED: npm run build failed before implementation because configureServerTimeouts and DEFAULT_SERVER_TIMEOUTS were missing exports.
• GREEN: focused timeout tests pass after implementation.

Verification

• npm run build passed.
• $env:NODE_ENV='test'; node --test dist/server-timeouts.test.js passed 4 tests.
• npx prettier --check README.md src/index.ts src/server-timeouts.test.ts passed.
• npm run lint passed.
• Cleaned dist/, rebuilt with npm run build, then $env:NODE_ENV='test'; node --test dist/*.test.js dist/**/*.test.js passed 93 tests across 11 suites.
• git diff --cached --check passed before commit.

Note: npm test uses POSIX-style NODE_ENV=test, so on Windows PowerShell I used the equivalent $env:NODE_ENV='test'; node --test ... commands.