chore: align repo scaffolding with the package standard

[TheGreatAxios]

Closes CL-9400

Summary

• LICENSE replaced with Interchange's LGPL-2.1 text (was the FSF text). 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), the custom corbits field and the overrides block (every dependency already resolves one drizzle-orm@0.45.2, and consumers never see a dependency's overrides); added engines bun >=1.2.0 alongside node >=24; test runs bun test src --pass-with-no-tests; added a check script; test:coverage stays as the coverage gate. @types/bun moves to 1.3.9 and @types/node is removed: the standard types: ["bun"] with the old 1.1.14 types clashed with Node 22's File/URL globals. Key order is oxfmt's sortPackageJson order.
• tsconfig.json and tsconfig.build.json use the shared templates. The paths alias for @corbits/artifacts is gone, so e2e/reference-host.test.ts and examples/reference-host import src/index.js by relative path. noUncheckedIndexedAccess needed ids[n]! in six e2e/list.test.ts assertions.
• .gitignore replaced with the shared template.
• test.yml replaced by the standard ci.yml: checkout v5, Node 24, Postgres 16 on port 5432, bun run check, then bun run test:coverage (src and e2e under the bunfig.toml 80% floor, which is kept) instead of test:e2e, then packs the tarball and imports createArtifactRoutes and runArtifactMigrations under Node. The e2e/helpers.ts default ARTIFACT_DATABASE_URL moves from port 5457 to 5432 to match.
• CONTRIBUTING cut from 406 to 25 lines (Development, CLA line, Postgres setup, Migrations, Commit messages). The design notes move to a new AGENTS.md (Purpose, Layout, Rules, the Internals sections unchanged). .github/SECURITY.md and 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).
• CHANGELOG.md removed; GitHub Releases track changes. The README changelog link goes with it.

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 SECURITY.md

Checks

bun run build, check, test:e2e (274 tests), test:coverage (292 tests, above the floor) on local Postgres, and the Node pack-and-import smoke pass locally.