The resolve-conflicts skill runs `jj resolve --tool mergiraf`, but the
sandbox image never installed it.

Assisted-by: Claude Sonnet 5 via Claude Code

diff --git a/.ramekin/Dockerfile b/.ramekin/Dockerfile
index fa970999..d317994f 100644
--- a/.ramekin/Dockerfile
+++ b/.ramekin/Dockerfile
@@ -9,4 +9,13 @@ RUN ARCH=$(uname -m) && \
     curl -fsSL "https://github.com/facebook/dotslash/releases/download/v0.5.8/dotslash-linux-musl.${DS_ARCH}.tar.gz" \
     | tar xz -C /usr/local/bin dotslash
 
+RUN ARCH=$(uname -m) && \
+    case "$ARCH" in \
+        aarch64) MF_ARCH="aarch64" ;; \
+        x86_64) MF_ARCH="x86_64" ;; \
+        *) echo "Unsupported architecture: $ARCH" && exit 1 ;; \
+    esac && \
+    curl -fsSL "https://codeberg.org/mergiraf/mergiraf/releases/download/v0.18.0/mergiraf_${MF_ARCH}-unknown-linux-gnu.tar.gz" \
+    | tar xz -C /usr/local/bin mergiraf
+
 COPY bin/shellcheck /usr/local/bin/shellcheck