UI/allow logo selection (#4982)

# Description of Changes

- Allow switching between logos in-app using the same section in
settings

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/src/core/components/shared/AppConfigModal.css

@@ -127,4 +127,45 @@
   display: flex;
   justify-content: flex-end;
   gap: 0.5rem;
+}
+
+/* Settings section container for sticky footer support */
+.settings-section-container {
+  display: flex;
+  flex-direction: column;
+  min-height: 100%;
+  position: relative;
+}
+
+.settings-section-content {
+  flex: 1;
+  padding-bottom: 5rem; /* Space for sticky footer */
+}
+
+/* Sticky footer for save/discard buttons */
+.settings-sticky-footer {
+  position: sticky;
+  bottom: 0;
+  left: 0;
+  right: 0;
+  background: var(--modal-content-bg);
+  border-top: 1px solid var(--modal-header-border);
+  padding: 1rem 2rem;
+  margin: 0 -2rem;
+  margin-bottom: -1rem;
+  z-index: 10;
+  box-shadow: 0 -4px 12px rgba(0, 0, 0, 0.1);
+}
+
+/* Mobile adjustments */
+@media (max-width: 1024px) {
+  .settings-sticky-footer {
+    padding: 0.75rem 1rem;
+    margin: 0 -1rem;
+    margin-bottom: -1rem;
+  }
+  
+  .settings-section-content {
+    padding-bottom: 4rem;
+  }
 }