Installs the packages needed to run justfile targets (fmt, clippy,
test, coverage) inside the ramekin container.

Assisted-by: GLM-5.1 via pi

diff --git a/.ramekin/Dockerfile b/.ramekin/Dockerfile
new file mode 100644
index 0000000..efa8486
--- /dev/null
+++ b/.ramekin/Dockerfile
@@ -0,0 +1,9 @@
+FROM ramekin-agent
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    bc \
+    cargo \
+    grcov \
+    jq \
+    rustc \
+    rustfmt \
+    && rm -rf /var/lib/apt/lists/*