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/identity-infrastructure.module.ts

@@ -31,6 +31,10 @@ import { RedisSessionCache } from './redis/redis-session.cache';
         requestTimeoutMs: Number(config.get('PIREON_TIMEOUT_MS', 5000)),
         clientId: config.get<string>('PIREON_CLIENT_ID') || undefined,
         clientSecret: config.get<string>('PIREON_CLIENT_SECRET') || undefined,
+        passwordClientId:
+          config.get<string>('PIREON_PASSWORD_CLIENT_ID') || undefined,
+        passwordClientSecret:
+          config.get<string>('PIREON_PASSWORD_CLIENT_SECRET') || undefined,
         scopes: String(config.get('PIREON_SCOPES', 'users:read'))
           .split(/\s+/)
           .filter(Boolean),