fix: UI Improvement in /devcard-demo - Fix Return Home button overlap

[anuragbraveboy-sudo]

Fixes #121

Problem

The /devcard-demo route did not exist, which meant the Return Home
The button had no proper page structure — causing it to overlap with
main content, especially on smaller screen sizes.

Root Cause

No /devcard-demo page existed in the codebase. The button had no
parent layout constraints, leading to overlap and broken UI.

Solution

✅ Created the missing /devcard-demo route with +page.svelte
✅ Used flexbox layout (flex-direction: column) so Return Home
button stays in normal document flow — no overlap possible
✅ Added top-bar div with proper padding and border separator
✅ Dark background (#0f1222) matching existing DevCard styling
✅ Responsive media queries for all breakpoints:

• 1024px — adjusted content padding
• 768px — reduced top-bar and content padding
• 480px — smaller button font and padding for mobile

Screenshots

Before Fix:

• /devcard-demo route did not exist — button had no proper styling or layout

After Fix:

• Return Home button clearly visible at top ✅
• Zero overlap with main content ✅
• Page renders correctly at /devcard-demo ✅

Testing

• pnpm lint → web app has no lint script (expected per CONTRIBUTING.md)
• pnpm test → web app has no test script (expected per CONTRIBUTING.md)
• Tested on desktop, tablet, and mobile viewports ✅