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)

AGENTS.md

@@ -0,0 +1,37 @@
+# AGENTS.md — TOTEM ZMK Config
+
+## Build
+
+Local Docker build (no GitHub Actions needed):
+
+```bash
+docker run --rm \
+  -v $(pwd):/workspace/zmk-config \
+  -w /workspace/zmk-config \
+  zmkfirmware/zmk-build-arm:stable \
+  bash -c "
+    git config --global --add safe.directory '*'
+    west zephyr-export
+    west build -s zmk/app -d build/left  -b xiao_ble -- -DSHIELD=totem_left  -DZMK_CONFIG=/workspace/zmk-config/config
+    west build -s zmk/app -d build/right -b xiao_ble -- -DSHIELD=totem_right -DZMK_CONFIG=/workspace/zmk-config/config
+  "
+
+cp build/left/zephyr/zmk.uf2  totem_left.uf2
+cp build/right/zephyr/zmk.uf2 totem_right.uf2
+```
+
+- Clean build dirs between config changes: `rm -rf build/left build/right`
+- The Docker image `zmkfirmware/zmk-build-arm:stable` must be pulled first (~3 GB)
+- Board name is `xiao_ble` (not `seeeduino_xiao_ble` — that was the old name)
+- `west update` only needed when ZMK/Zephyr deps change (pulls submodules)
+- `CONFIG_ZMK_BLE=y` is explicitly set in `config/totem.conf` (board defconfig alone proved unreliable)
+
+## Keymap
+
+The active keymap is `config/totem.keymap`. It overrides the shield default at `config/boards/shields/totem/totem.keymap`.
+
+3 layers: `BASE` (0), `UML` (1), `BT` (2).
+
+## BINDINGS.md
+
+**After every binding change** in `config/totem.keymap`, update `BINDINGS.md` with an ASCII graphic of all three layers and the quick-reference table. The physical key labels in the ASCII art must match the BASE layer positions exactly.