feat: Enable Custom S3 storage provider option

Replaces the disabled 'S3 Compatible' placeholder with an active 'Custom S3' option in the profile modal storage settings. This maps to the 'generic_s3' provider which is already supported by the backend logic.

- Updated `components/profile-modal.html` to enable the option.
- Verified via script and visual inspection (headless screenshot).
- Verified existing tests pass.

components/profile-modal.html

@@ -826,7 +826,7 @@
                             <span class="mb-2 block font-medium">Provider</span>
                             <select id="storageProvider" class="input">
                                 <option value="cloudflare_r2" selected>Cloudflare R2</option>
-                                <option value="aws_s3" disabled>S3 Compatible (Coming Soon)</option>
+                                <option value="generic_s3">Custom S3</option>
                             </select>
                         </label>