Add configurable hotkey (alternative to Ctrl+Alt+V)

[turqoisehex]

Summary

The toggle hotkey is hardcoded to Ctrl+Alt+V in poll_hotkey() (line ~84). Some users may have conflicts with this key combination or prefer a different shortcut.

Acceptance Criteria

• Add a --hotkey CLI argument (e.g., --hotkey "ctrl+alt+d")
• Parse the hotkey string into virtual key codes
• Update poll_hotkey() to use the configured keys instead of hardcoded VK_CONTROL + VK_MENU + VK_V
• Default remains Ctrl+Alt+V when no flag is provided
• Update README and --help output

Relevant Code

• Virtual key code constants: hushtype.py lines ~73-78
• poll_hotkey(): hushtype.py line ~84
• GetAsyncKeyState polling: hushtype.py lines ~89-95

Notes

The hotkey system uses Win32 GetAsyncKeyState polling (not keyboard hooks), so the implementation needs to map key names to VK_ constants. A simple lookup table for common modifiers (ctrl, alt, shift) and letter keys would suffice.