build: add a manifest and build workflow

.github/workflows/build.yml

@@ -0,0 +1,29 @@
+name: Firmware build
+
+on:
+  push:
+  schedule:
+    - cron: '0 4 * * *'
+  workflow_dispatch:
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Zephyr project
+        uses: zephyrproject-rtos/action-zephyr-setup@main
+        with:
+          app-path: firmware
+          toolchains: arm-zephyr-eabi
+
+      - name: Build
+        run: |
+          west build firmware

firmware/west.yml

@@ -0,0 +1,14 @@
+manifest:
+  remotes:
+    - name: zephyrproject-rtos
+      url-base: https://github.com/zephyrproject-rtos
+
+  projects:
+    - name: zephyr
+      remote: zephyrproject-rtos
+      revision: main
+      import:
+        name-allowlist:
+          - cmsis
+          - hal_nordic
+          - tinycrypt