chore: align repo scaffolding with the package standard

[TheGreatAxios]

Closes CL-9396

Summary

• LICENSE: already the Interchange text (unchanged); add CLA.md and the cla.yml CLA Assistant workflow
• package.json: drop main/types (exports covers Node 24 and Bun); add keywords and engines (bun and node); homepage points at #readme; scripts are the standard set: build clears dist first, test runs bun test src --pass-with-no-tests and test:e2e runs e2e, and a new check runs typecheck, lint, format check and unit tests. Key order is oxfmt's
• tsconfig.json and tsconfig.build.json follow the standard templates: drops allowImportingTsExtensions and composite, adds noImplicitOverride, exactOptionalPropertyTypes and moduleDetection. No source changes were needed
• .gitignore: standard list (drops .tmp and *.log; adds *.tgz, coverage/, .env.*)
• ci.yml (new; the repo had no CI): a Postgres 16 service with the libpq PG* variables the e2e harness reads, bun run check, bun run test:e2e, then a pack-and-import smoke under Node 24 that checks createHookRoutes, createRunTriggerDeliverer, createTenantSystemSender and isRunTriggerUnroutable
• CONTRIBUTING.md: the standard template plus a CLA line and the real-Postgres e2e paragraph with a one-line Postgres start; the "How a hook fires" notes move to AGENTS.md
• AGENTS.md (new): purpose, layout, rules (run principal, system sender, no unsigned mode) and local development
• README: drop the npm and license badges

Stacked on #19.

• CONTRIBUTING gets a Releasing section: releases are manual, as in Interchange (npm version, push tags, gh release create --generate-notes, npm publish).

Commits

1. chore: add the CLA
2. build: align package.json and tsconfig with the package standard
3. ci: run check and a Node pack smoke
4. docs: trim CONTRIBUTING, add AGENTS.md, drop README badges

Checks

bun run build, bun run check and bun run test:e2e (against local Postgres) pass; the Node pack smoke passes locally.