feat: harden plugin api for separate repos, signed updates and generic external login

packages/plugin-sdk/client.d.ts

@@ -0,0 +1,13 @@
+/**
+ * Import forms `termix-plugin build` understands beyond plain modules. Picked
+ * up through tsconfig.plugin.json.
+ */
+
+/** A script copied next to the bundle; the import is its URL. */
+declare module "*?url" {
+  const url: string;
+  export default url;
+}
+
+/** A stylesheet imported for its side effect; the build emits frontend.css. */
+declare module "*.css";