Add admin identity module: better-auth, per-app permissions, invitations (#12)

Reviewed-on: #12
Co-authored-by: Patrick Müller <mail@pmueller.me>
Co-committed-by: Patrick Müller <mail@pmueller.me>

vitest.config.ts

@@ -3,6 +3,9 @@ import {defineConfig} from 'vitest/config';
 export default defineConfig({
 	test: {
 		include: ['test/**/*.test.ts'],
+		// The integration suite needs a Docker MariaDB and runs separately via
+		// npm run test:integration (vitest.integration.config.ts).
+		exclude: ['test/integration/**'],
 		environment: 'node',
 		// feedback.ratelimit throws at import time without a salt (see
 		// test/feedback/ratelimit.salt-guard.test.ts). Set one here so the suite