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>

.env.example

@@ -18,10 +18,14 @@ EVENTS_BRIDGE_ENABLED=true
 PIREON_BASE_URL=https://oauth.pireon.dev
 # Secret returned when registering the webhook (POST /api/clients/{client}/webhooks)
 PIREON_WEBHOOK_SECRET=
-# OAuth client registered for task-stream (POST /api/clients). Needed by the web app to sign in.
-# Redirect URI to register: http://localhost:4200/auth/callback
+# OAuth clients of task-stream in Pireon (POST /api/clients). Each Pireon client allows ONE grant type:
+#   authorization_code → "Sign in with Pireon" and Swagger UI. Redirect URIs to register:
+#     http://localhost:4200/auth/callback, http://localhost:3000/api/docs/oauth2-redirect.html
 PIREON_CLIENT_ID=
 PIREON_CLIENT_SECRET=
+#   password → email + password sign-in (defaults to the client above when empty)
+PIREON_PASSWORD_CLIENT_ID=
+PIREON_PASSWORD_CLIENT_SECRET=
 PIREON_SCOPES=users:read
 PIREON_PASSWORD_GRANT=true
 AUTH_SESSION_TTL_SECONDS=60