feat(web): complete V21 UI redesign for all pages

- Replaced Ant Design Card/Layout with V21-compliant components
- Updated Header, MainLayout to V21 sticky top navigation
- Redesigned WorkspaceList, ProjectAssets, ProjectResults, ProjectTitles, ProjectVoices, ProjectGeneration with V21 card/grid system
- Added V21 color scheme, typography, spacing, pill badges, vertical/video cards
- Updated Login page and Plans subscription page to V21 design
- CSS-only styling without Ant Design overrides where possible

apps/web/src/components/layout/Header.css

@@ -0,0 +1,87 @@
+/* V21 顶导 */
+.xx-top-nav {
+  height: 68px;
+  position: sticky;
+  top: 0;
+  z-index: 30;
+  background: rgba(255, 255, 255, 0.86);
+  backdrop-filter: blur(16px);
+  border-bottom: 1px solid rgba(226, 232, 240, 0.92);
+}
+
+.xx-top-nav-inner {
+  max-width: 1440px;
+  margin: 0 auto;
+  height: 100%;
+  padding: 0 24px;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.xx-brand {
+  display: flex;
+  gap: 10px;
+  align-items: center;
+  font-size: 20px;
+  font-weight: 900;
+  border: none;
+  background: none;
+  cursor: pointer;
+  color: #0f172a;
+  padding: 0;
+}
+
+.xx-logo {
+  width: 38px;
+  height: 38px;
+  border-radius: 14px;
+  background: linear-gradient(135deg, #818cf8, #4f46e5);
+  display: grid;
+  place-items: center;
+  color: #fff;
+  box-shadow: 0 12px 26px rgba(79, 70, 229, 0.24);
+  font-size: 20px;
+}
+
+.xx-nav-links {
+  display: flex;
+  gap: 23px;
+  color: #64748b;
+  font-weight: 750;
+}
+
+.xx-nav-links button {
+  border: none;
+  background: none;
+  cursor: pointer;
+  color: #64748b;
+  padding: 0;
+  font-size: 14px;
+  font-weight: 750;
+  transition: color 0.2s;
+}
+
+.xx-nav-links button:hover {
+  color: #4f46e5;
+}
+
+.xx-nav-links button.active {
+  color: #4f46e5;
+}
+
+.xx-user-menu {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  cursor: pointer;
+  color: #0f172a;
+  font-size: 14px;
+}
+
+.xx-avatar {
+  width: 34px;
+  height: 34px;
+  background: #eef2ff;
+  color: #4338ca;
+}