feat: introduce apply button functionality (v0.1)

### Summary
- Added a new "Apply" button to code snippets provided by the AI assistant.
- The button is designed to seamlessly merge the AI-generated snippet into the relevant file in the editor.

### Current Issues
1. **Sticky Accept/Decline Buttons:** These activate for every snippet instead of being limited to the relevant snippet.
2. **Discard Button:** Currently non-functional.
3. **Highlight Inconsistencies:** The green-red code highlights for old and new code are inconsistent.

### To Do
- Implement a toast notification when the "Apply" button is pressed on an irrelevant tab to prevent code application errors.

### Workflow Implemented
1. The "Apply" button is added alongside "Copy" and "Reply" for AI-generated code snippets.
2. Upon clicking "Apply," the code snippet and relevant file content (active file) are sent to a secondary model (GPT-4O).
3. The system prompt for GPT-4O instructs it to merge the snippet with the file content:
   - Ensure the original file functionality remains intact.
   - Integrate the code snippet seamlessly.
4. The output from GPT-4O is injected directly into the code editor.
5. Changes are visually highlighted:
   - Green for new code.
   - Red for removed code.
6. Highlights remain until the user explicitly accepts or discards the changes.

frontend/app/globals.css

@@ -175,3 +175,23 @@
 .tab-scroll::-webkit-scrollbar {
   display: none;
 }
+
+.added-line-decoration {
+  background-color: rgba(0, 255, 0, 0.1);
+}
+
+.removed-line-decoration {
+  background-color: rgba(255, 0, 0, 0.1);
+}
+
+.added-line-glyph {
+  background-color: #28a745;
+  width: 4px !important;
+  margin-left: 3px;
+}
+
+.removed-line-glyph {
+  background-color: #dc3545;
+  width: 4px !important;
+  margin-left: 3px;
+}