chore: fix chat ui bugs (#38105)

/ok-to-test tags="@tag.Anvil"

<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/12275840983>
> Commit: 558f4684ed8b43e7290715e8461ef4510a3aec87
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=12275840983&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Anvil`
> Spec:
> <hr>Wed, 11 Dec 2024 12:19:21 UTC
<!-- end of auto-generated comment: Cypress test results  -->


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
	- Enhanced button styling in the sidebar for non-mobile view.
	- Introduced a new expand button for the sidebar header.

- **Bug Fixes**
- Improved layout and visibility of sidebar elements, ensuring proper
alignment and display.

- **Style**
	- Added minimum height to the sidebar header.
	- Implemented styles to hide empty sidebar headers. 
	- Adjusted margin for the sidebar header expand button. 
	- Removed horizontal overflow property from sidebar content.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/client/packages/design-system/widgets/src/components/Sidebar/src/SidebarContent.tsx

@@ -46,6 +46,7 @@ const _SidebarContent = (
           )}
           {!isMobile && (
             <Button
+              className={styles.sidebarHeaderExpandButton}
               color="neutral"
               icon={
                 state === "full-width"

app/client/packages/design-system/widgets/src/components/Sidebar/src/styles.module.css

@@ -152,7 +152,6 @@
 .sidebarContentInner {
   flex-grow: 1;
   overflow-y: auto;
-  overflow-x: hidden;
   width: 100%;
 }
 
@@ -163,13 +162,22 @@
  */
 .sidebarHeader {
   height: var(--sizing-13);
+  min-height: var(--sizing-13);
   padding: 0 var(--inner-spacing-2);
   border-bottom: var(--border-width-1) solid var(--color-bd-elevation-1);
 }
 
+.sidebarHeader:empty {
+  display: none;
+}
+
 .sidebarTitle {
   position: absolute;
   left: 0;
   right: 0;
   margin: 0 var(--sizing-14);
 }
+
+.sidebarHeaderExpandButton {
+  margin-inline-start: auto;
+}