Show onboarding banner to link to YT video & do not show release note on first-time (#1490)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Adds an onboarding banner in Setup that links to a 3-minute YouTube
intro and dismisses after click. Also avoids showing release notes on a
user’s first launch.

- **New Features**
- Added OnboardingBanner component with YouTube thumbnail and play icon.
  - Opens the video via IpcClient and hides the banner after click.
  - Integrated into SetupBanner with local visibility state.

- **Bug Fixes**
  - Don’t show release notes on first run to prevent spam.

<!-- End of auto-generated description by cubic. -->

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds a dismissible onboarding banner linking to a YouTube intro and
changes release notes to appear only on app updates, not first run.
> 
> - **UI/Onboarding**:
> - **`src/components/home/OnboardingBanner.tsx`**: New banner component
with YouTube thumbnail/play icon; opens intro video via
`IpcClient.openExternalUrl`; hides itself on click.
> - **`src/components/SetupBanner.tsx`**: Integrates `OnboardingBanner`
with `isOnboardingVisible` state; tweaks header typography
(`font-medium`).
> - **Release Notes Behavior**:
> - **`src/pages/home.tsx`**: Only shows release notes when upgrading
(checks existing `settings.lastShownReleaseNotesVersion` before opening
modal); preserves themed URL handling.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
832e70f87b3b6a7e8b8b921fe8c6ceb15198cce0. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

src/components/home/OnboardingBanner.tsx

@@ -0,0 +1,56 @@
+import { IpcClient } from "@/ipc/ipc_client";
+import { Play } from "lucide-react";
+
+export const OnboardingBanner = ({
+  isVisible,
+  setIsVisible,
+}: {
+  isVisible: boolean;
+  setIsVisible: (isVisible: boolean) => void;
+}) => {
+  if (!isVisible) return null;
+
+  return (
+    // <div className="fixed top-0 left-0 right-0 z-50 flex justify-center mt-2">
+    <div className="max-w-xl w-full mx-4 relative mb-4">
+      <a
+        onClick={(e) => {
+          e.preventDefault();
+          IpcClient.getInstance().openExternalUrl(
+            "https://www.youtube.com/watch?v=rgdNoHLaRN4",
+          );
+          setIsVisible(false);
+        }}
+        target="_blank"
+        rel="noopener noreferrer"
+        className="cursor-pointer block bg-(--background-lightest) border border-border rounded-lg shadow-lg hover:bg-accent transition-colors"
+      >
+        <div className="flex items-center">
+          <div className="relative p-2">
+            <img
+              src="https://img.youtube.com/vi/rgdNoHLaRN4/maxresdefault.jpg"
+              alt="Get started with Dyad in 3 minutes"
+              className="w-28 h-16 object-cover rounded-md"
+            />
+            <div className="absolute inset-0 flex items-center justify-center">
+              <div className="w-10 h-10 bg-background rounded-full flex items-center justify-center shadow-md">
+                <Play size={20} className="text-foreground ml-0.5" />
+              </div>
+            </div>
+          </div>
+          <div className="flex-1 px-4 py-3">
+            <div className="text-foreground">
+              <p className="font-semibold text-base">
+                Get started with Dyad in 3 minutes
+              </p>
+              <p className="text-sm text-muted-foreground">
+                Start building your app for free
+              </p>
+            </div>
+          </div>
+        </div>
+      </a>
+    </div>
+    // </div>
+  );
+};