Remove mouse support functionality

[markparonyan]

This pull request removes all mouse support functionality from dvtm, simplifying the codebase by eliminating mouse event handling, configuration, and related keybindings.

Summary

Mouse support has been completely removed from dvtm. This includes the mouse event handling infrastructure, button bindings, configuration options, and all related command-line flags and keybindings.

Key Changes

• Removed mouse infrastructure:

  • Deleted Button typedef and buttons[] array from config
  • Removed mouse_setup() function and mouse initialization
  • Removed handle_mouse() event handler
  • Removed vt_mouse() function from terminal emulator

• Removed mouse-related commands:

  • Deleted togglemouse() command
  • Deleted mouse_focus(), mouse_fullscreen(), mouse_minimize(), and mouse_zoom() helper functions
  • Removed mouse command keybinding (MOD-M)

• Removed mouse state tracking:

  • Deleted msel (mouse-selected client) variable
  • Deleted mouse_events_enabled flag
  • Deleted mousetrack field from Vt struct
  • Removed CSI mode 1000 (mouse tracking) handling

• Removed command-line interface:

  • Removed -M flag for toggling mouse support at startup
  • Updated help text and argument parsing

• Removed documentation:

  • Removed mouse commands section from man page
  • Removed copy/paste workaround documentation from README
  • Removed mouse button event descriptions

• Code cleanup:

  • Removed debug logging for mouse events
  • Removed mouse-related preprocessor conditionals and compatibility definitions
  • Removed extensive mouse button constant documentation from config