keymap: Colemak UML layer with arrows, BT combos, fix BLE/settings config

- UML layer: arrows on T(↑) C(←) D(↓) V(→), ALT on Enter
- BT profile switching via combos: CTRL+Q/W/F/P → profiles 1-4
- Explicit CONFIG_ZMK_BLE, CONFIG_FLASH, CONFIG_NVS, CONFIG_SETTINGS_NVS
- Board name: seeeduino_xiao_ble → xiao_ble
- Add .gitignore, AGENTS.md (build docs), BINDINGS.md (keymap ref)

config/boards/shields/totem/totem.zmk.yml

@@ -3,7 +3,7 @@ id: totem
 name: TOTEM
 type: shield
 url: https://github.com/GEIGEIGEIST/TOTEM
-requires: [seeeduino_xiao_ble]
+requires: [xiao_ble]
 features:
   - keys
 siblings: