[BLD-26] Portal: AI Chat UI improvements (#7764)

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## PR-Codex overview
This PR primarily focuses on enhancing the UI components and improving the styling, particularly around the `ScrollShadow` component. It also introduces new animations and adjusts various layouts for better responsiveness.

### Detailed summary
- Removed `ScrollShadow.tsx` and its CSS module.
- Updated color in `NextTopLoader` from `--link-foreground` to `--foreground`.
- Added `sonner` package for toasts.
- Integrated `ScrollShadow` in multiple components.
- Adjusted layout styles in `page.tsx` and `MarkdownRenderer.tsx`.
- Enhanced `Chat` component with `ScrollShadow` for better scrolling behavior.
- Introduced `TextShimmer` and `UnderlineLink` components.
- Improved styling and responsiveness in various components.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

* **New Features**
  * Introduced a shimmering text effect for loading states.
  * Added a customizable toast notification system with theme support.
  * Added an underlined link component for consistent link styling.

* **Enhancements**
  * Refined chat interface with improved empty state, message rendering, feedback handling, and visual distinction between user and AI messages.
  * Updated markdown rendering for improved link, heading, list, and paragraph styles.
  * Improved icon rendering with unique ID management and monochrome support.
  * Adjusted chat page and loader bar styling for better layout and color consistency.

* **Bug Fixes**
  * Corrected React key usage in code snippet rendering to use unique platform IDs.

* **Refactor**
  * Modularized chat message rendering and feedback logic.
  * Updated import paths for scroll shadow components across multiple files.

* **Chores**
  * Updated dependencies to include the "sonner" package.
  * Cleaned up whitespace, formatting, and removed unused lint comments.
  * Adjusted Tailwind configuration for border radius and added shimmer animation.

* **Removals**
  * Deleted legacy scroll shadow component and associated CSS.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: MananTank

apps/portal/package.json

@@ -34,6 +34,7 @@
     "remark-gfm": "4.0.1",
     "server-only": "^0.0.1",
     "shiki": "1.27.0",
+    "sonner": "2.0.6",
     "tailwind-merge": "^2.6.0",
     "tailwindcss-animate": "^1.0.7",
     "thirdweb": "workspace:*",

apps/portal/src/app/chat/page.tsx

@@ -8,7 +8,7 @@ const queryClient = new QueryClient();
 export default function ChatPage() {
   return (
     <QueryClientProvider client={queryClient}>
-      <div className="m-auto flex h-[calc(100vh-4rem)] w-full flex-col overflow-hidden lg:size-[calc(100vh-8rem)]">
+      <div className="flex h-[calc(100vh-65px)] flex-col overflow-hidden lg:h-[calc(100vh-102px)]">
         <Chat />
       </div>
     </QueryClientProvider>

apps/portal/src/app/layout.tsx

@@ -43,7 +43,7 @@ export default function RootLayout({
           enableSystem={false}
         >
           <NextTopLoader
-            color="hsl(var(--link-foreground))"
+            color="hsl(var(--foreground))"
             height={2}
             shadow={false}
             showSpinner={false}