feat(FN-3087): document graph plugin in plugin authoring guide

Documentation-only finish for FN-3087, adding changeset and README updates for the dependency graph plugin and plugin authoring guide.

Fusion-Task-Id: FN-3087

plugins/fusion-plugin-dependency-graph/src/__tests__/DependencyGraph.test.tsx

@@ -117,4 +117,11 @@ describe("DependencyGraph", () => {
     fireEvent.click(screen.getByTestId("task-A"));
     expect(onOpenDetail).toHaveBeenCalledWith(expect.objectContaining({ id: "A" }));
   });
+
+  it("falls back to onOpenTaskDetail when onOpenDetail is not provided", () => {
+    const onOpenTaskDetail = vi.fn();
+    render(<DependencyGraph tasks={[createTask("A", "in-progress")]} onOpenTaskDetail={onOpenTaskDetail} />);
+    fireEvent.click(screen.getByTestId("task-A"));
+    expect(onOpenTaskDetail).toHaveBeenCalledWith("A");
+  });
 });

plugins/fusion-plugin-dependency-graph/src/__tests__/GraphTaskNode.drag.test.tsx

@@ -40,6 +40,19 @@ afterEach(() => {
 });
 
 describe("GraphTaskNode drag", () => {
+  it("does not open detail after drag threshold is exceeded", () => {
+    const onOpenDetail = vi.fn();
+    render(<GraphTaskNode {...props({ onOpenDetail })} />);
+    const node = screen.getByTestId("graph-task-node-FN-1");
+
+    fireEvent.pointerDown(node, { pointerId: 1, clientX: 10, clientY: 10, isPrimary: true });
+    fireEvent.pointerMove(node, { pointerId: 1, clientX: 25, clientY: 25, isPrimary: true });
+    fireEvent.pointerUp(node, { pointerId: 1, clientX: 25, clientY: 25, isPrimary: true });
+    fireEvent.click(node);
+
+    expect(onOpenDetail).not.toHaveBeenCalled();
+  });
+
   it("applies dragging class only after threshold move", () => {
     const onNodePositionChange = vi.fn();
     render(<GraphTaskNode {...props({ onNodePositionChange })} />);

plugins/fusion-plugin-dependency-graph/src/__tests__/host-integration.test.ts

@@ -11,7 +11,7 @@ describe("dependency graph plugin host integration contract", () => {
       expect.objectContaining({
         viewId: "graph",
         label: "Graph",
-        componentPath: "./src/DependencyGraph.tsx",
+        componentPath: "./dashboard-view",
         placement: "more",
       }),
     ]);