feat(FN-3726): highlight fast mode bolt icon in task detail

- Add TaskDetailModal CSS rules to visually emphasize the fast mode bolt icon
- Cover fast mode icon highlighting in TaskDetailModal rendering tests
- Preserve existing modal rendering behavior while adding the new fast mode visual cue

Fusion-Task-Id: FN-3726

packages/dashboard/app/components/TaskDetailModal.css

@@ -219,6 +219,14 @@
   color: var(--color-warning);
 }
 
+.detail-execution-mode-toggle--fast svg {
+  color: var(--color-warning);
+  background: color-mix(in srgb, var(--color-warning) 20%, transparent);
+  border-radius: var(--radius-pill);
+  padding: var(--space-xs);
+  box-shadow: var(--glow-warning);
+}
+
 .detail-execution-mode-toggle--saving {
   opacity: 0.75;
 }

packages/dashboard/app/components/__tests__/TaskDetailModal.rendering.test.tsx

@@ -324,6 +324,7 @@ describe("TaskDetailModal", () => {
       const toggle = screen.getByRole("button", { name: "Execution mode: standard" });
       expect(toggle).toHaveAttribute("aria-pressed", "false");
       expect(toggle).toHaveTextContent("Standard");
+      expect(toggle).not.toHaveClass("detail-execution-mode-toggle--fast");
     });
 
     it("renders fast mode as a pressed toggle", () => {
@@ -342,9 +343,21 @@ describe("TaskDetailModal", () => {
       const toggle = screen.getByRole("button", { name: "Execution mode: fast" });
       expect(toggle).toHaveAttribute("aria-pressed", "true");
       expect(toggle).toHaveTextContent("Fast");
+      expect(toggle).toHaveClass("detail-execution-mode-toggle--fast");
     });
   });
 
+  it("defines fast execution mode svg highlight styles with warning tokens", () => {
+    const css = readDashboardStylesSource();
+
+    expectBaseRule(css, ".detail-execution-mode-toggle--fast svg", "color: var(--color-warning);");
+    expectBaseRule(
+      css,
+      ".detail-execution-mode-toggle--fast svg",
+      "background: color-mix(in srgb, var(--color-warning) 20%, transparent);",
+    );
+  });
+
   it("appends daemon token query to attachment href/src URLs for direct browser loads", () => {
     localStorage.setItem("fn.authToken", "daemon-token");