WIP: Add CLI for OAuth login, update README

- Add src/cli.ts with login command for OAuth providers
- Add bin entry to package.json for 'npx @mariozechner/pi-ai'
- Update README: remove setApiKey docs, rewrite OAuth section
- OAuth storage is caller's responsibility, not library's
- Use getOAuthProviders() instead of duplicating provider list

packages/ai/package.json

@@ -5,6 +5,9 @@
 	"type": "module",
 	"main": "./dist/index.js",
 	"types": "./dist/index.d.ts",
+	"bin": {
+		"pi-ai": "./dist/cli.js"
+	},
 	"files": [
 		"dist",
 		"README.md"