chore: add build pipeline

.github/workflows/build.yaml

@@ -0,0 +1,57 @@
+name: Badgebagic Firmware build
+
+on:
+  push:
+  pull_request:
+    branches: [master]
+
+env:
+  MRS_TOOLCHAIN: MRS_Toolchain_Linux_x64_V1.91
+  BUILD_DIR: build
+  BIN_TYPES: '{.bin,.elf}'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Cache toolchain
+        id: cache-toolchain
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.MRS_TOOLCHAIN }}
+          key: ${{ env.MRS_TOOLCHAIN }}-cache
+
+      - name: Download toolchain
+        if: steps.cache-toolchain.outputs.cache-hit != 'true'
+        run: |
+          wget http://file-oss.mounriver.com/tools/${{ env.MRS_TOOLCHAIN }}.tar.xz
+          tar -xvf ${{ env.MRS_TOOLCHAIN }}.tar.xz
+
+      - name: Build firmware
+        run: |
+          export PREFIX=${{ env.MRS_TOOLCHAIN }}/RISC-V_Embedded_GCC/bin/riscv-none-embed-
+          make
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: badgemagic-firmware
+          path: ${{ env.BUILD_DIR }}/badgemagic-*
+
+      - name: Upload firmware binaries to bin branch
+        # Skip upload APK for pull requests & only allow binaries build from master
+        if: ${{ github.event_name != 'pull_request' && github.ref_name == 'master' }}
+        run: |
+          git config --global user.name "${{ github.workflow }}"
+          git config --global user.email "gh-actions@${{ github.repository_owner }}"
+
+          mv ${{ env.BUILD_DIR }}/badgemagic-*${{ env.BIN_TYPES }} ./
+          
+          git checkout --orphan temporary
+          git add badgemagic-*${{ env.BIN_TYPES }}
+          git commit -am "[Auto] Update firmware binaries from ${{ github.ref_name }} ($(date +%Y-%m-%d.%H:%M:%S))"
+          git branch -D bin || true
+          git branch -m bin
+          git push --force origin bin
+