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>

apps/api/src/app/config.schema.ts

@@ -23,9 +23,13 @@ export const configSchema = Joi.object({
   // Pireon identity server
   PIREON_BASE_URL: Joi.string().uri().default('https://oauth.pireon.dev'),
   PIREON_WEBHOOK_SECRET: Joi.string().allow('').optional(),
-  // OAuth client of task-stream in Pireon, used by the web app to sign in.
+  // OAuth clients of task-stream in Pireon (each Pireon client allows one grant type):
+  // authorization_code for "Sign in with Pireon" / Swagger UI…
   PIREON_CLIENT_ID: Joi.string().allow('').optional(),
   PIREON_CLIENT_SECRET: Joi.string().allow('').optional(),
+  // …and password for email + password (defaults to the client above).
+  PIREON_PASSWORD_CLIENT_ID: Joi.string().allow('').optional(),
+  PIREON_PASSWORD_CLIENT_SECRET: Joi.string().allow('').optional(),
   PIREON_SCOPES: Joi.string().default('users:read'),
   PIREON_PASSWORD_GRANT: Joi.boolean().default(true),
   PIREON_TIMEOUT_MS: Joi.number().default(5000),