fix: Download Badge button remains enabled but performs no action in GitHub Action mode (JhaSourav07#1759)

## Description

Fixes JhaSourav07#1725 

### Summary

The **Download Badge** button remained enabled in **GitHub Action**
export mode even though badge downloads were not supported for that
export type. This created a confusing user experience because the button
appeared functional but performed no action.

### Changes Made

* Disabled the **Download Badge** button when GitHub Action export mode
is selected.
* Added disabled styling to visually indicate that the action is
unavailable.
* Updated the button text to **"Download Not Available"**.
* Improved accessibility by providing a descriptive `aria-label` for the
disabled state.

### Testing

* Verified Markdown export remains unaffected.
* Verified HTML export remains unaffected.
* Verified GitHub Action export displays a disabled button with clear
messaging.
* Ran `npm run lint` successfully (warnings only, no errors).
* Verified changes locally on the customization page.

## Pillar

* [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

### Before

* Download Badge button remained enabled in GitHub Action mode.
* Clicking the button did not download any file.
<img width="1440" height="438" alt="Screenshot 2026-05-30 at 5 34 18 PM"
src="https://github.com/user-attachments/assets/a203b42a-2d00-45f4-8651-a4aa69109f9b"
/>
<img width="1440" height="900" alt="Screenshot 2026-05-30 at 5 34 01 PM"
src="https://github.com/user-attachments/assets/aacfdc45-bb40-41dd-a71d-677de25d8daf"
/>

### After

* Download Badge button is disabled in GitHub Action mode.
* Button label clearly indicates that downloading is unavailable.
<img width="726" height="749" alt="Screenshot 2026-05-30 at 8 26 49 PM"
src="https://github.com/user-attachments/assets/43611c13-0b3e-467f-8972-34973a1ac7c2"
/>
<img width="726" height="749" alt="Screenshot 2026-05-30 at 8 27 01 PM"
src="https://github.com/user-attachments/assets/44e11e49-a569-4b9b-8399-8aa93cff944b"
/>
<img width="726" height="749" alt="Screenshot 2026-05-30 at 8 27 17 PM"
src="https://github.com/user-attachments/assets/daa304fe-4036-4835-82c9-cca78227a6de"
/>


## 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=YOUR_USERNAME`).
* [ ] 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): ...`).
* [x] 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.
* [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard.
* [ ] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

app/customize/components/ExportPanel.tsx

@@ -165,15 +165,17 @@ export function ExportPanel({
           <button
             type="button"
             onClick={handleDownloadBadge}
-            disabled={!hasUsername || isDownloading}
+            disabled={!hasUsername || isDownloading || format === 'action'}
             aria-label={
-              hasUsername
-                ? 'Download custom monolith layout as an image'
-                : 'Add a GitHub username to enable image downloads'
+              !hasUsername
+                ? 'Add a GitHub username to enable image downloads'
+                : format === 'action'
+                  ? 'Download is not available in GitHub Action mode'
+                  : 'Download custom monolith layout as an image'
             }
             className={`relative inline-flex items-center gap-2 px-4 py-2 rounded-xl text-xs font-bold transition-all duration-200 ${
-              !hasUsername || isDownloading
-                ? 'bg-gray-200/90 border border-black/10 text-gray-500 cursor-not-allowed dark:bg-white/10 dark:border-white/10 dark:text-white/60'
+              !hasUsername || isDownloading || format === 'action'
+                ? 'bg-gray-200/90 border border-black/10 text-gray-500 cursor-not-allowed dark:bg-white/10 dark:border-white/10 dark:text-white/35'
                 : 'bg-emerald-500/10 border border-emerald-500/30 text-emerald-500 hover:bg-emerald-500/20 hover:scale-[1.03] active:scale-[0.97]'
             }`}
           >
@@ -198,7 +200,11 @@ export function ExportPanel({
                 </>
               )}
             </svg>
-            {isDownloading ? 'Downloading...' : 'Download Badge'}
+            {format === 'action'
+              ? 'Download Not Available'
+              : isDownloading
+                ? 'Downloading...'
+                : 'Download Badge'}
           </button>
 
           {/* Clipboard Copy Button */}