fix(auth): separate Pireon clients for authorization code and password

Pireon OAuth clients allow a single grant type. With one PIREON_CLIENT_ID of
type password, email + password worked but "Sign in with Pireon" failed with
`unauthorized_client`.

- PIREON_CLIENT_ID/SECRET: authorization_code client (Sign in with Pireon,
  Swagger UI). New PIREON_PASSWORD_CLIENT_ID/SECRET: password client, falling
  back to the former so existing setups keep working.
- Refresh tries both clients: a refresh token only works with its issuer.
- PIREON_PASSWORD_GRANT=false now also rejects password grants in the API
  (before it only hid the form).
- /api/auth/config returns clientId: null when there is no authorization_code
  client, and the web hides "Sign in with Pireon".
- docker-compose passes the new variables; docs 05/07, .env.example,
  openapi.json; unit tests for the client selection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/identity/infrastructure/src/lib/adapters/browser-authorization.flow.ts

@@ -21,6 +21,8 @@ export class BrowserAuthorizationFlow extends AuthorizationFlow {
   private readonly document = inject(DOCUMENT);
 
   async start(config: AuthConfig, returnUrl: string): Promise<void> {
+    if (!config.clientId)
+      throw new Error('Pireon sign-in is not configured on the API');
     const codeVerifier = randomString(64);
     const state = randomString(32);
     sessionStorage.setItem(