Add clearer placeholder and helper text to explain that encrypted environment
variables are never displayed for security reasons. When editing an existing
server, the encrypted_env field shows a placeholder explaining that leaving it
blank will preserve existing values.
Also apply cargo fmt formatting fixes to store.rs.
- Add env_config field to McpServer, CreateMcpServerRequest, UpdateMcpServerRequest
- Encrypt env_config using encrypt_token() on create/update
- Decrypt env_config in get_server_env_config() helper function
- Handle clearing env_config with empty string
- Add comprehensive tests:
- test_env_config_encrypted_at_rest()
- test_update_env_config()
- test_clear_env_config_with_empty_string()
- test_env_config_none_preserves_existing()
All tests passing. Follows same encryption pattern as auth_value.
