Add footer_height method to PanelContent trait with default 0. Implement
footer_height in FormulaContent to return 1 when in FormulaEdit mode.
Update Panel::render to subtract footer height from item height. This
enables optional footers in panels.
Co-Authored-By: fiddlerwoaroof/git-smart-commit (bartowski/nvidia_Nemotron-Cascade-2-30B-A3B-GGUF)
Refactor AppMode to use MinibufferConfig for all text-entry modes. Update
command implementations to use new mode constructors. Introduce
PanelContent trait and replace panel structs with content types. Adjust
rendering to use Panel::new and minibuffer configuration. Update imports
and add MinibufferConfig struct. No functional changes; all behavior
preserved.
Co-Authored-By: fiddlerwoaroof/git-smart-commit (bartowski/nvidia_Nemotron-Cascade-2-30B-A3B-GGUF)
