fix(app): comprehensive mobile UX improvements

[Indosaram]

What does this PR do?

This PR provides comprehensive mobile UX and layout improvements for the web application. Key enhancements include:

• Touch-friendly Sidebar Scrolling: Implemented touch event handlers to distinguish between tap and drag gestures in the session list. Vertical movement exceeding 10px now correctly identifies a scroll action and prevents accidental navigation.
• Mobile Layout Optimizations: Adjusted padding, button gaps, and icon sizes (specifically fixing the submit button to 16x16px) for mobile viewports to maximize usable space.
• Reliability & Connectivity: Added a visibility change listener to automatically reconnect the event stream and refresh project data when the app resumes from the background. Improved the scroll-to-bottom retry logic to be more resilient on mobile devices.
• Viewport & CSS Fixes: Added viewport-fit=cover and safe-area CSS support for notched devices. Disabled user-scaling and fixed overscroll behaviors to provide a more native app-like experience.
• Feature Additions: Added a mobileSendOnEnter setting to allow users to configure keyboard behavior on mobile devices.

How did you verify your code works?

Manual Verification. Verified all layout adjustments and the sidebar auto-close behavior using the Vite development server.