Responsiveness with grid system

[craigyu]

Description

To ensure responsiveness across different devices, we need to integrate Bootstrap's grid system for easier development. The grid system should start with the <main> container. The <main> container should have the container class from Bootstrap, and every child component should use the appropriate classes such as row, col, or col-*.

Acceptance Criteria

• Implement the grid system across the app.
• Remove the unnecessary <div> wrapper outside <main>.
• Remove padding in <main> to prevent other components from needing negative margins to achieve full width.