Enhancement: Keyboard Shortcuts Modal

[Pranav00076]

Description:
We have several keyboard shortcuts (V, H, R, C, T, Backspace), but no way for the user to discover them.

How to Implement:

1. Modal UI: Create a sleek dialog component (e.g., using Radix UI or native <dialog>) listing all available shortcuts and their actions.
2. Trigger: Add a small "?" or "Keyboard Shortcuts" button in the bottom right corner of the canvas. Also, allow opening the modal by pressing the ? key (Shift + /).
3. Content: Document standard tools (V = Select, H = Hand/Pan, etc.) and global shortcuts (Delete/Backspace to delete, Ctrl+Z to undo, etc.).