feat: implement URL plugins with table/row actions and prefill support

- Add URL plugin effects (register, export_url, clear_urls) in core
- Add PluginHostnameInfo, HostnameMetadata::Plugin, and plugin registration types
- Implement plugin URL table in web UI with tableAction button and rowAction overflow menus
- Thread urlPluginMetadata (packageId, hostId, interfaceId, internalPort) as prefill to actions
- Add prefill support to PackageActionData so metadata passes through form dialogs
- Add i18n translations for plugin error messages
- Clean up plugin URLs on package uninstall

core/src/registry/package/get.rs

@@ -602,6 +602,7 @@ fn check_matching_info_short() {
             os_version: exver::Version::new([0, 3, 6], []),
             sdk_version: None,
             hardware_acceleration: false,
+            plugins: BTreeSet::new(),
         },
         icon: DataUrl::from_vec("image/png", vec![]),
         dependency_metadata: BTreeMap::new(),