test: expand markdown and post menu coverage

Adds focused regression coverage for quote previews, markdown link rendering, embed toggles, and desktop/mobile post-menu actions. It also fixes the undefined feed-state crash in use-state-string.ts and removes unnecessary runtime imports with import type.

src/components/loading-ellipsis/__tests__/loading-ellipsis.test.tsx

@@ -0,0 +1,44 @@
+import * as React from 'react';
+import { createElement } from 'react';
+import { createRoot, type Root } from 'react-dom/client';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import LoadingEllipsis from '../loading-ellipsis';
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+const act = (React as { act?: (cb: () => void | Promise<void>) => void | Promise<void> }).act as (cb: () => void | Promise<void>) => void | Promise<void>;
+
+let container: HTMLDivElement;
+let root: Root;
+
+describe('LoadingEllipsis', () => {
+  beforeEach(() => {
+    container = document.createElement('div');
+    document.body.appendChild(container);
+    root = createRoot(container);
+  });
+
+  afterEach(() => {
+    act(() => root.unmount());
+    container.remove();
+  });
+
+  it('keeps the last word inside the nowrap span and preserves the prefix text', () => {
+    act(() => {
+      root.render(createElement(LoadingEllipsis, { string: 'Downloading board' }));
+    });
+
+    const spans = container.querySelectorAll('span');
+    expect(container.textContent).toBe('Downloading board');
+    expect(spans[1]?.textContent).toBe('board');
+    expect(spans[2]).toBeTruthy();
+  });
+
+  it('renders single-word strings without a leading space', () => {
+    act(() => {
+      root.render(createElement(LoadingEllipsis, { string: 'Loading' }));
+    });
+
+    expect(container.textContent).toBe('Loading');
+    expect(container.firstChild?.textContent).toBe('Loading');
+  });
+});