feat(KB-063): add realtime GitHub badge updates

- Add a focused GitHub badge poller with shared rate-limit, freshness, and cleanup handling
- Wire a dedicated badge websocket server and routes to stream PR and issue badge snapshots
- Add a shared useBadgeWebSocket hook and update TaskCard to subscribe only when visible while preserving partial badge state
- Cover polling, websocket, and task card flows with tests and document the realtime badge channel

packages/dashboard/app/components/Header.test.tsx

@@ -21,8 +21,8 @@ function renderHeader(props = {}) {
 describe("Header", () => {
   it("renders the logo and brand", () => {
     renderHeader();
-    expect(screen.getByText("kb")).toBeDefined();
-    expect(screen.getByText("board")).toBeDefined();
+    expect(screen.getByText("Fusion")).toBeDefined();
+    expect(screen.getByText("tasks")).toBeDefined();
   });
 
   it("renders action buttons", () => {