Init: Corne-only zmk-config

Extracted from zmk-config-archive (multi-board repo).
Corne 42-key with nice_nano_v2, nice_oled, RGB, ZMK Studio, Javelin steno.

boards/shields/corne/corne.zmk.yml

@@ -0,0 +1,18 @@
+file_format: "1"
+id: corne
+name: Corne
+type: shield
+url: https://github.com/foostan/crkbd/
+requires: [pro_micro]
+exposes: [i2c_oled]
+features:
+  - keys
+  - display
+  - underglow
+  - studio
+siblings:
+  - corne_left
+  - corne_right
+  - corne_left_peripheral
+  - corne_dongle_xiao
+  - corne_dongle_pro_micro