Ctrl+Z should undo instead of suspending session

## Problem
Using Ctrl+Z (universal undo shortcut) suspends the session without warning, causing loss of work progress.

## Expected Behavior
Ctrl+Z should undo the last action (like in any text editor/IDE)

## Current Behavior
Ctrl+Z immediately suspends session with no recovery option

## Impact

• Breaks muscle memory from other editors
• No warning before losing work
• No easy way to restore suspended session
• Disrupts development flow

## Suggested Solutions

1. Map Ctrl+Z to undo functionality
2. Use different shortcut for suspend (e.g., Ctrl+Shift+Z)
3. Add confirmation dialog before suspending
4. Implement session auto-save/restore