chore: align repo scaffolding with the package standard

[TheGreatAxios]

Closes CL-9391

Summary

• LICENSE replaced with Interchange's LGPL-2.1 text (was the FSF text with an extra header). CLA.md and the CLA Assistant workflow (cla.yml, signatures on a cla-signatures branch) added; CONTRIBUTING links the CLA.
• package.json: dropped main/types (exports covers Node and Bun), added keywords, homepage#readme, engines bun >=1.2.0 alongside node >=24, build clears dist first, test runs bun test src --pass-with-no-tests and test:e2e runs bun test e2e, and a check script; key order is oxfmt's sortPackageJson order.
• tsconfig.json and tsconfig.build.json use the shared templates (drops allowImportingTsExtensions and the build comment; adds exactOptionalPropertyTypes, noImplicitOverride, moduleDetection). The one error it surfaced: runCronMigrations passed ssl: config.ssl (possibly undefined) to postgres; it now passes config.ssl ?? false, which is the driver's default.
• .gitignore replaced with the shared template.
• New ci.yml (the repo had no CI): one Node 24 job with a Postgres 16 service that runs bun run check, bun run test:e2e, then packs the tarball and imports createCronRoutes, createCronTicker and isValidCronExpression under Node.
• CONTRIBUTING trimmed to the standard (Development with the CLA line and the e2e line, Migrations, Commit messages). The Internals notes moved to a new AGENTS.md. README badges removed.
• 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: use the Interchange LICENSE text and 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, check (typecheck, lint, format:check, test) and the Node pack-and-import smoke pass locally. test:e2e passes against local Postgres (9 tests), with no extra timeout flag.

• test: e2e database setup hooks get a 60s timeout (DB_SETUP_TIMEOUT_MS); a fresh database plus every migration can outlast bun's 5s default.