[FEATURE] Add ESC key to close help popup

[ascender1729]

Description

Add keyboard support to close the help popup/modal by pressing the ESC key.

Why Needed

• Standard UX pattern for modals
• Improves accessibility
• Faster interaction for keyboard users

Implementation Details

• Listen for 'keydown' event on document when modal is open
• Check if key is 'Escape' (key code 27)
• Call close function when ESC pressed
• Clean up event listener when modal closes

Files to Modify

• src/components/shared/HelpButton.svelte or modal component

Acceptance Criteria

• ESC key closes help popup when open
• No effect when popup is already closed
• Works across all major browsers
• Event listener properly cleaned up

Time Estimates

• With AI: 45 minutes
• Without AI: 300 minutes