feat(FN-3704): separate plugin lifecycle from setup probe state

Fixes a bug where plugin lifecycle operations were incorrectly gated by the setup probe state, separating the two concerns across the API, PluginManager component, routes, and tests, with updated documentation.

Fusion-Task-Id: FN-3704

packages/dashboard/src/plugin-routes.ts

@@ -406,8 +406,10 @@ export function createPluginRouter(
 
     if (plugin.state !== "started") {
       res.json({
-        hasSetup: false,
-        status: { status: "error", error: "Plugin not loaded" },
+        hasSetup: true,
+        setupCheckDeferred: true,
+        deferredReason: "plugin-not-started",
+        pluginState: plugin.state,
       });
       return;
     }