Fix CI: install tools natively instead of using Docker-in-Docker

Volume mounts with -v $PWD:/src fail when the runner itself runs
inside a container (the path exists in the runner container but not
on the Docker daemon host). Switch all four jobs to native apt-get
installs of the same packages that are in the Dockerfile. The
container-based just recipes remain unchanged for local use.

.gitea/workflows/ci.yml

@@ -6,9 +6,6 @@ on:
   pull_request:
     branches: [main]
 
-env:
-  IMAGE: ptt-builder
-
 jobs:
   build:
     name: Build firmware
@@ -18,25 +15,18 @@ jobs:
         with:
           submodules: recursive
 
-      - name: Build container image
-        run: docker build -t $IMAGE .
+      - name: Install toolchain
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install -y --no-install-recommends \
+            gcc-arm-none-eabi binutils-arm-none-eabi libnewlib-arm-none-eabi \
+            cmake ninja-build
 
       - name: Compile firmware
-        run: |
-          docker run --rm \
-            --user "$(id -u):$(id -g)" \
-            -v "$PWD:/src" \
-            $IMAGE \
-            sh -c "cmake -B /src/build -G Ninja \
-                         -DCMAKE_BUILD_TYPE=MinSizeRel /src \
-                   && ninja -C /src/build"
+        run: cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=MinSizeRel . && ninja -C build
 
       - name: Print size
-        run: |
-          docker run --rm \
-            -v "$PWD:/src" \
-            $IMAGE \
-            arm-none-eabi-size /src/build/firmware
+        run: arm-none-eabi-size build/firmware
 
   format:
     name: Check formatting
@@ -44,18 +34,15 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Build container image
-        run: docker build -t $IMAGE .
+      - name: Install clang-format
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install -y --no-install-recommends clang-format
 
       - name: clang-format check
         run: |
-          docker run --rm \
-            --user "$(id -u):$(id -g)" \
-            -v "$PWD:/src" \
-            $IMAGE \
-            sh -c "find /src/src /src/include -name '*.c' -o -name '*.h' | \
-                   xargs clang-format --dry-run --Werror \
-                         --style=file:/src/.clang-format"
+          find src include -name '*.c' -o -name '*.h' | \
+            xargs clang-format --dry-run --Werror --style=file:.clang-format
 
   lint:
     name: Static analysis
@@ -63,22 +50,20 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Build container image
-        run: docker build -t $IMAGE .
+      - name: Install cppcheck
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install -y --no-install-recommends cppcheck
 
       - name: cppcheck
         run: |
-          docker run --rm \
-            --user "$(id -u):$(id -g)" \
-            -v "$PWD:/src" \
-            $IMAGE \
-            sh -c "cppcheck --error-exitcode=1 \
+          cppcheck --error-exitcode=1 \
                    --enable=warning,style,performance,portability \
                    --suppress=missingInclude \
                    --inline-suppr \
                    --std=c11 \
-                            -I /src/include \
-                            /src/src/"
+                   -I include \
+                   src/
 
   docs:
     name: Build documentation
@@ -86,14 +71,12 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Build container image
-        run: docker build -t $IMAGE .
+      - name: Install Doxygen
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install -y --no-install-recommends doxygen
 
       - name: Doxygen
         run: |
-          docker run --rm \
-            --user "$(id -u):$(id -g)" \
-            -v "$PWD:/src" \
-            $IMAGE \
-            sh -c "cd /src && doxygen Doxyfile 2>&1 | tee /tmp/doxy.log && \
-                   ! grep -q 'warning:' /tmp/doxy.log"
+          doxygen Doxyfile 2>&1 | tee /tmp/doxy.log
+          ! grep -q 'warning:' /tmp/doxy.log