add sidebar toggle/close button on home page for mobile

### Self Checks

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### 1. Is this request related to a challenge you're experiencing? Tell me about your story.

On mobile devices, the home page sidebar is always open with no way to close
it. It takes up most of the screen width, making the main content difficult
to read.

App detail pages have a sidebar toggle icon (looks like a small panel/battery
icon) on the right side of the top bar that lets users collapse the sidebar.
The home page does not have this icon, so mobile users cannot close the sidebar.

Steps to reproduce:
1. Open Dify on mobile (or Chrome DevTools → iPhone 14 Pro Max)
2. Go to the home page (/) → sidebar is always open, no toggle icon
3. Navigate to any app → notice the sidebar toggle icon on the right side
of the top bar

### 2. Additional context or comments

### 3. Can you help us with this feature?

- [x] I am interested in contributing to this feature.

Start at the home page entry point (/), then compare its sidebar and top-bar behavior with the sidebar toggle shown on app detail pages. Identify the existing toggle implementation and determine where the home page needs equivalent access; done means mobile users can open and close the sidebar without obscuring the main content.

Written by the indexing model from the issue text.