feat(chat): port chat widget components from Dart to React

src/app/chat/components/language-dialog.module.css

@@ -0,0 +1,66 @@
+/* LanguageDialog 语言切换弹窗样式 */
+
+.overlay {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.5);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 50;
+}
+
+.dialog {
+  width: calc(100% - 40px);
+  max-width: 360px;
+  background: var(--color-surface, #1f1a2e);
+  border-radius: var(--radius-lg, 12px);
+  padding: var(--spacing-5, 20px);
+  display: flex;
+  flex-direction: column;
+  gap: var(--spacing-3, 12px);
+  max-height: 80vh;
+}
+
+.title {
+  font-size: var(--font-size-lg, 18px);
+  font-weight: 600;
+  margin: 0;
+  color: var(--color-text-primary, #fff);
+}
+
+.list {
+  display: flex;
+  flex-direction: column;
+  gap: var(--spacing-1, 4px);
+  overflow-y: auto;
+  max-height: 60vh;
+}
+
+.item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--spacing-3, 12px) var(--spacing-4, 16px);
+  background: transparent;
+  border: 0;
+  border-radius: var(--radius-md, 8px);
+  color: var(--color-text-primary, #fff);
+  font-size: var(--font-size-base, 14px);
+  text-align: left;
+  cursor: pointer;
+}
+
+.item:hover,
+.item:focus-visible {
+  background: rgba(255, 255, 255, 0.05);
+}
+
+.itemActive {
+  background: rgba(248, 77, 150, 0.15);
+}
+
+.check {
+  color: var(--color-accent, #f84d96);
+  font-weight: 700;
+}