[codex] Paginate API-key and webhook lists

[pq198363-ops]

Summary

Closes #146.

• Add shared bounded limit/offset parsing for list endpoints.
• Paginate GET /api/v1/api-keys with a total count while preserving prefix-only key list items.
• Paginate GET /api/v1/webhooks with a total count while preserving webhook item shape.
• Sort both lists by createdAt and then internal id for stable paging.
• Document the pagination contract in the README and OpenAPI route summaries.

RED/GREEN

RED before implementation:

npm run build
NODE_ENV=test node --test dist/list-pagination.test.js

tests 2
pass 0
fail 2
failure: total was undefined on api-keys and webhooks list responses

GREEN after implementation:

npm run build
NODE_ENV=test node --test dist/list-pagination.test.js

tests 2
pass 2
fail 0

Verification

npx prettier --check README.md src/pagination.ts src/routes/apiKeys.ts src/routes/webhooks.ts src/routes/meta.ts src/list-pagination.test.ts
All matched files use Prettier code style!

npm run lint
eslint .

npm run build
NODE_ENV=test node --test dist/list-pagination.test.js
tests 2
pass 2
fail 0

NODE_ENV=test node --test dist/*.test.js dist/**/*.test.js
tests 91
pass 91
fail 0

git diff --check

Note: on Windows PowerShell I used the direct $env:NODE_ENV='test'; node --test ... equivalent after npm run build because the package npm test script uses POSIX-style NODE_ENV=test syntax.