FN-5855: fix frozen dashboard spinners

Restore shared spinner animation behavior for dashboard AI activity indicators.

- switch BackgroundTasksIndicator loaders to the shared animate-spin utility class
- anchor shared spin utilities on SVG centers with transform-origin and transform-box rules
- add CSS regression tests covering global spin keyframes and spinner utility styles

Files changed:
 .../app/__tests__/spinner-animation.css.test.ts    | 50 ++++++++++++++++++++++
 .../app/components/BackgroundTasksIndicator.tsx    |  9 ++--
 packages/dashboard/app/styles.css                  |  7 +++
 3 files changed, 60 insertions(+), 6 deletions(-)

Fusion-Task-Id: FN-5855

Fusion-Task-Lineage: b94d4333-2e78-4c4b-a304-5a13b797bbc6

packages/dashboard/app/__tests__/spinner-animation.css.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import { readFileSync } from "fs";
+import { resolve } from "path";
+
+function extractBlock(content: string, pattern: RegExp): string {
+  const match = content.match(pattern);
+  expect(match?.index).toBeDefined();
+
+  const start = match!.index! + match![0].length;
+  let index = start;
+  let depth = 1;
+
+  while (index < content.length && depth > 0) {
+    if (content[index] === "{") depth += 1;
+    if (content[index] === "}") depth -= 1;
+    index += 1;
+  }
+
+  expect(depth).toBe(0);
+  return content.slice(match!.index!, index);
+}
+
+describe("global spinner animation utility", () => {
+  const css = readFileSync(resolve(__dirname, "../styles.css"), "utf8");
+
+  it("keeps top-level spin keyframes rotating to 360deg", () => {
+    const topLevelSpinBlock = extractBlock(css, /@keyframes\s+spin\s*\{/);
+
+    expect(topLevelSpinBlock).toContain("transform: rotate(360deg);");
+    expect(css.indexOf("@keyframes spin")).toBeLessThan(css.indexOf(":root {\n  --bg:"));
+  });
+
+  it("keeps the shared animate-spin and spin utilities running infinitely", () => {
+    const animateSpinBlock = css.match(/\.animate-spin\s*\{[\s\S]*?\}/)?.[0] ?? "";
+    const spinBlock = css.match(/\.spin\s*\{[\s\S]*?\}/)?.[0] ?? "";
+
+    expect(animateSpinBlock).toContain("animation: spin 1s linear infinite;");
+    expect(spinBlock).toContain("animation: spin 1s linear infinite;");
+  });
+
+  it("anchors SVG spinners around their own center", () => {
+    const animateSpinBlock = css.match(/\.animate-spin\s*\{[\s\S]*?\}/)?.[0] ?? "";
+    const spinBlock = css.match(/\.spin\s*\{[\s\S]*?\}/)?.[0] ?? "";
+    const svgSpinnerBlock = css.match(/svg\.animate-spin,\s*svg\.spin\s*\{[\s\S]*?\}/)?.[0] ?? "";
+
+    expect(animateSpinBlock).toContain("transform-origin: center;");
+    expect(spinBlock).toContain("transform-origin: center;");
+    expect(svgSpinnerBlock).toContain("transform-box: fill-box;");
+  });
+});

packages/dashboard/app/components/BackgroundTasksIndicator.tsx

@@ -119,7 +119,7 @@ export function BackgroundTasksIndicator({
         title={`${total} background AI task${total !== 1 ? "s" : ""}${needsInput > 0 ? ` (${needsInput} need${needsInput !== 1 ? "" : "s"} input)` : ""}`}
       >
         {generating > 0 && (
-          <Loader2 size={12} style={{ animation: "spin 1s linear infinite" }} />
+          <Loader2 size={12} className="animate-spin" />
         )}
         {needsInput > 0 && generating === 0 && <HelpCircle size={12} />}
         <span>AI {total}</span>
@@ -188,11 +188,8 @@ export function BackgroundTasksIndicator({
                   {isGenerating && (
                     <Loader2
                       size={14}
-                      className="background-tasks-indicator__session-icon"
-                      style={{
-                        animation: "spin 1s linear infinite",
-                        color: "var(--color-success)",
-                      }}
+                      className="background-tasks-indicator__session-icon animate-spin"
+                      style={{ color: "var(--color-success)" }}
                     />
                   )}
                   {isAwaiting && !activeElsewhere && (

packages/dashboard/app/styles.css

@@ -187,10 +187,17 @@ html {
 }
 .animate-spin {
   animation: spin 1s linear infinite;
+  transform-origin: center;
 }
 
 .spin {
   animation: spin 1s linear infinite;
+  transform-origin: center;
+}
+
+svg.animate-spin,
+svg.spin {
+  transform-box: fill-box;
 }
 
 :root {