ci: Add ESP-IDF firmware build job

.gitea/workflows/lint.yml

@@ -1,4 +1,4 @@
-name: Lint & Security
+name: Lint & Build
 
 on:
   push:
@@ -7,6 +7,25 @@ on:
     branches: [main]
 
 jobs:
+  build:
+    name: Build Firmware
+    runs-on: anvil
+    container:
+      image: docker.io/espressif/idf:v5.3
+    steps:
+      - name: Checkout
+        run: |
+          git clone --depth=1 --branch=${{ github.ref_name }} \
+            https://oauth2:${{ github.token }}@git.mymx.me/${{ github.repository }}.git .
+
+      - name: Build firmware
+        run: |
+          cd get-started/csi_recv_router
+          idf.py build
+
+      - name: Show binary size
+        run: |
+          ls -lh get-started/csi_recv_router/build/*.bin
   cppcheck:
     name: C/C++ Static Analysis
     runs-on: anvil