Makes the nine layout constants self-documenting by showing which value
controls which part of the window (cell size, menu bar, panel margin,
side panel, and overall window dimensions).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Splits the flat 432-line main.rs into four modules so each file has one
clear job: render.rs owns layout constants and drawing primitives,
editor.rs owns EditorTab/EditorState and the side panel, glyph_picker.rs
owns the floating picker dialog with a decoupled (open, glyph) interface,
and main.rs is reduced to AppMode, App, and the frame loop (~150 lines).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
randrews