feat(ui): swap AI-chat and comments icons to avoid confusion

The AI chat button used IconSparkles and the page comments button used
IconMessage, which read as visually similar speech bubbles. Replace the
AI icon with IconMessageCircleStar (chat bubble + star) and the comments
icon with IconMessages (overlapping bubbles) so the two are clearly
distinct.

- app-header.tsx: IconSparkles -> IconMessageCircleStar
- page-header-menu.tsx: IconMessage -> IconMessages

apps/client/src/components/layouts/global/app-header.tsx

@@ -5,7 +5,7 @@ import {
   Text,
   Tooltip,
 } from "@mantine/core";
-import { IconSparkles } from "@tabler/icons-react";
+import { IconMessageCircleStar } from "@tabler/icons-react";
 import classes from "./app-header.module.css";
 import { BrandLogo } from "@/components/ui/brand-logo";
 import TopMenu from "@/components/layouts/global/top-menu.tsx";
@@ -107,7 +107,7 @@ export function AppHeader() {
                 aria-label={t("AI chat")}
                 onClick={() => setAiChatWindowOpen((v) => !v)}
               >
-                <IconSparkles size={20} />
+                <IconMessageCircleStar size={20} />
               </ActionIcon>
             </Tooltip>
           )}

apps/client/src/features/page/components/header/page-header-menu.tsx

@@ -10,7 +10,7 @@ import {
   IconLink,
   IconList,
   IconMarkdown,
-  IconMessage,
+  IconMessages,
   IconPrinter,
   IconStar,
   IconStarFilled,
@@ -111,7 +111,7 @@ export default function PageHeaderMenu({ readOnly }: PageHeaderMenuProps) {
           aria-label={t("Comments")}
           {...commentsTriggerProps}
         >
-          <IconMessage size={20} stroke={2} />
+          <IconMessages size={20} stroke={2} />
         </ActionIcon>
       </Tooltip>