- Add Section 8 describing GlyphLayout data structure and feedback path
- Renderer captures byte offsets, X/Y positions, and advance widths during shaping
- Layout flows via layoutChan to logic goroutine, replacing lastLineYChan
- Editor uses layout for accurate cursor rendering and navigation
- Handles word wrap, screen resize, editing, scroll, and non-fixed-width fonts
- Replace gtx.Event(nil) with key.Filter{Focus: focusedID} and
key.FocusFilter{Target: focusedID} so Gio correctly routes key
and edit events to the focused editor text field.
- Convert EditorState.CursorPosition (byte offset) to line/column
coordinates for accurate cursor rendering.
- Add debug logging in HandleKeyDown and HandleCursorMove.
