fix(ui): add cursor-pointer and hover animation to Copy Link button (JhaSourav07#978)

## Description
Fixes JhaSourav07#969

The `Copy Link` button on the Contribution Story page lacked hover
animations and cursor feedback, making it feel non-interactive. This fix
adds proper hover and active state styling to the button.

**Changes made:**
- Added `cursor-pointer` so the cursor changes to a pointer on hover
- Added `transform` and `hover:scale-105` for a subtle scale-up effect
on hover
- Added `hover:brightness-125` for visible brightness feedback on hover
- Added `hover:border-white/30` for a border highlight on hover
- Added `active:scale-95` for a click/press feedback effect
- Fixed in both `components/dashboard/ShareSheet.tsx` and `app/page.tsx`
- Separated the Copy Link button into its own explicit JSX branch so
Tailwind JIT compiler can detect all utility classes correctly

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## Pillar
- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

---

## Visual Preview


https://github.com/user-attachments/assets/de73b3bd-3733-4d35-9005-d04c7c3498ac


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## Checklist before requesting a review:
- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=Pranav-IIITM`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [ ] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [ ] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

app/page.tsx

@@ -238,7 +238,7 @@ export default function LandingPage() {
                 <button
                   type="submit"
                   disabled={!mounted || !hasUsername}
-                  className={`relative flex min-w-[160px] items-center justify-center gap-2 overflow-hidden rounded-xl px-6 py-3.5 text-sm font-semibold transition-all duration-200 active:scale-[0.98] ${
+                  className={`relative flex min-w-[160px] items-center justify-center gap-2 overflow-hidden rounded-xl px-6 py-3.5 text-sm font-semibold transition-all duration-200 transform cursor-pointer hover:scale-105 hover:brightness-125 active:scale-[0.98] disabled:cursor-not-allowed ${
                     hasUsername
                       ? 'bg-black text-white hover:bg-zinc-800 dark:bg-white dark:text-black dark:hover:bg-zinc-100'
                       : 'bg-gray-200 text-gray-500 dark:bg-white/10 dark:text-white/35'