fix(oauth): fix login failures and add provider icon_url config

- Fix FIND_OAUTH_LINKED_USER_SQL missing allowed_providers_mode columns
- Fix TOUCH_OAUTH_LINK_SQL json/jsonb type mismatch in COALESCE
- Add icon_url field to OAuth provider config (DB, API, frontend)
- Fix admin OAuth test: accept 404 as reachable, use system proxy

apps/aether-gateway/src/handlers/admin/request/system/import.rs

@@ -1885,6 +1885,7 @@ impl<'a> AdminAppState<'a> {
                         oauth_provider.extra_config,
                         "extra_config",
                     )),
+                    icon_url: None,
                     is_enabled: oauth_provider.is_enabled,
                 };
                 invalid!(record.validate().map_err(|err| err.to_string()));