fix(FN-2688): add root dir to plugin install mock task store

- Add getRootDir() to the plugin command mock TaskStore used by createPluginLoader
- Ensure fn plugin install can resolve project root expectations without runtime failures
- Add a patch changeset for @runfusion/fusion documenting the CLI fix

.changeset/fn-2688-plugin-install-mock-taskstore.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Fix `fn plugin install` failing in CLI plugin commands by adding `getRootDir()` to the mock TaskStore used by `createPluginLoader`.

packages/cli/src/commands/plugin.ts

@@ -53,6 +53,7 @@ async function createPluginLoader(
   const projectPath = await getProjectPath(projectName);
   // Create a mock TaskStore for the loader (plugins don't need full task store access)
   const mockTaskStore = {
+    getRootDir: () => projectPath,
     getFusionDir: () => projectPath + "/.fusion",
     on: () => {},
     off: () => {},