Feature: Stack multiple layers into single diagram with corner legends

[hollowhemlock]

Feature: Stack multiple layers into single diagram with corner legends

Summary

Add a stack-layers command that combines multiple keyboard layers into a single compact diagram with corner legends. This creates reference diagrams showing up to 5 layers at once.

Motivation

When documenting keyboard layouts, having separate diagrams for each layer can be overwhelming. A stacked view shows the base layer prominently while indicating what each key does on other layers via small corner legends.

urob's keymap https://github.com/urob/zmk-config

Proposed Solution

New command: keymap stack-layers

keymap stack-layers --center Base --tl Fun --tr Sys --bl Num --br Nav keymap.yaml > stacked.yaml
keymap draw stacked.yaml > stacked.svg

Features

• Corner positions: Place up to 4 layers in corners (tl, tr, bl, br) around a center layer
• Hidden legends: Filter out values like modifiers (⇧, ⌃, ⌥, ⌘) from corners via config
• Glyph support: Corner legends can use glyphs (e.g., $$mdi:arrow-up$$)
• Combo inclusion: --include-combos LAYER... to include combos from specific layers with deduplication
• Separate combo layer: --separate-combo-layer to create a stacked_combos layer for overlay diagrams

New config section: stack_config

stack_config:
  hidden_corner_legends: [⇧, ⌃, ⌥, ⌘, sticky]
  hidden_held_legends: []
  hidden_shifted_legends: []

CSS styling

Corner legends use classes tl, tr, bl, br for text and glyphs:

text.tl { fill: #F93827; font-size: 8px; }
use.tl { fill: #F93827; }

Additional Context

See STACKED.md for full documentation.