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/api/identity/infrastructure/src/lib/pireon/pireon.config.ts

@@ -4,10 +4,17 @@ export interface PireonConfig {
   /** Seconds a resolved token is trusted before asking Pireon again. */
   sessionTtlSeconds: number;
   requestTimeoutMs: number;
-  /** OAuth client of task-stream in Pireon (Authorization Code + PKCE / password grant). */
+  /**
+   * Pireon OAuth client with grant type `authorization_code` ("Sign in with
+   * Pireon", Swagger UI). Pireon clients allow a single grant type, so email +
+   * password uses its own client below.
+   */
   clientId?: string;
   /** Kept server-side: browsers sign in through /api/auth/token. */
   clientSecret?: string;
+  /** Pireon OAuth client with grant type `password`; defaults to the one above. */
+  passwordClientId?: string;
+  passwordClientSecret?: string;
   scopes: string[];
   passwordGrant: boolean;
 }