Add ToolTip class (modules/ui_tooltip.py) and wire descriptive hover
tooltips onto every button, switch, slider, and dropdown in the main
window. Tooltips appear after a 500ms hover delay and are clamped to
screen bounds.
This requires no new dependencies — ToolTip uses only customtkinter.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>