Fix firmware release workflow: docker cp instead of a bind-mount

The runner's job workspace lives in a named Docker volume, not a real
host path, so a nested docker run -v "\$PWD:/workspace" bind-mounted an
empty directory when talking to the host daemon (which has no notion of
paths inside the calling container) -- build_for_board.sh: No such file
or directory. docker create/cp/start streams the checkout into the
build container through the Docker API instead, which works regardless
of what backs either side's workspace.

.gitea/workflows/firmware-release-build.yml

@@ -19,10 +19,11 @@ jobs:
     # the job specifies, so checkout fails immediately with "node: not
     # found" (hit this on the first real run). Checkout instead runs on the
     # plain runner (which has Node), and only the two build steps below
-    # spin up the ESP-IDF image themselves via `docker run` -- the runner
-    # already bind-mounts the host's docker socket, so docker-in-docker
-    # works fine from an ordinary run: step (same mechanism the existing
-    # server-docker-build.yml relies on for docker buildx).
+    # spin up the ESP-IDF image themselves (docker create/cp/start, see the
+    # comment on those steps for why not a plain `docker run -v`) -- the
+    # runner already bind-mounts the host's docker socket, so docker-in-
+    # docker works fine from an ordinary run: step (same mechanism the
+    # existing server-docker-build.yml relies on for docker buildx).
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -39,33 +40,45 @@ jobs:
       # set-target first since a fresh checkout has no cached sdkconfig
       # (firmware/sdkconfig* is gitignored, see firmware/.gitignore).
       # safe.directory guards against git's "dubious ownership" check,
-      # since the container runs as root over a volume owned by the
-      # runner's host user; idf.py shells out to git for component/
-      # version bookkeeping even though the embedded app version itself
-      # comes from version.txt, not git describe.
+      # since the container runs as root over content owned by a
+      # different uid.
+      #
+      # Deliberately `docker create`/`docker cp`/`docker start`, NOT
+      # `docker run -v "$PWD:/workspace"` -- the runner's own job
+      # workspace lives in a named Docker volume, not a real host path
+      # (confirmed from a failed run's container-inspect output), so a
+      # nested `docker run` bind-mounting "$PWD" talks to the *host*
+      # daemon about a path that only means something inside this job's
+      # own container -- it silently bind-mounted an empty directory,
+      # hence "build_for_board.sh: No such file or directory". `docker
+      # cp` streams files through the Docker API instead, so it works
+      # regardless of what backs either side's workspace.
       - name: Build (devkit -- ESP32-C6-DevKitC-1)
         run: |
-          docker run --rm -v "$PWD:/workspace" -w /workspace/firmware espressif/idf:release-v5.3 bash -c '
+          mkdir -p /tmp/release-assets
+          cid=$(docker create -w /workspace/firmware espressif/idf:release-v5.3 bash -c '
             git config --global --add safe.directory /workspace &&
             . "$IDF_PATH/export.sh" &&
             ./build_for_board.sh devkit set-target esp32c6 &&
             ./build_for_board.sh devkit build
-          '
+          ')
+          docker cp "$PWD/." "$cid:/workspace"
+          docker start -a "$cid"
+          docker cp "$cid:/workspace/firmware/build/espresso_frame.bin" /tmp/release-assets/firmware-devkit.bin
+          docker rm "$cid"
 
       - name: Build (xiao -- Seeed XIAO ESP32-C6)
         run: |
-          docker run --rm -v "$PWD:/workspace" -w /workspace/firmware espressif/idf:release-v5.3 bash -c '
+          cid=$(docker create -w /workspace/firmware espressif/idf:release-v5.3 bash -c '
             git config --global --add safe.directory /workspace &&
             . "$IDF_PATH/export.sh" &&
             ./build_for_board.sh xiao set-target esp32c6 &&
             ./build_for_board.sh xiao build
-          '
-
-      - name: Collect binaries
-        run: |
-          mkdir -p /tmp/release-assets
-          cp firmware/build/espresso_frame.bin /tmp/release-assets/firmware-devkit.bin
-          cp firmware/build_xiao/espresso_frame.bin /tmp/release-assets/firmware-xiao.bin
+          ')
+          docker cp "$PWD/." "$cid:/workspace"
+          docker start -a "$cid"
+          docker cp "$cid:/workspace/firmware/build_xiao/espresso_frame.bin" /tmp/release-assets/firmware-xiao.bin
+          docker rm "$cid"
 
       # Plain stdlib urllib rather than `requests` -- not guaranteed to be
       # pip-installed in the IDF image, and this is simple enough not to