refactor: use host runners/agent-runner/ in container instead of duplicate code

container/build.sh

@@ -1,10 +1,11 @@
 #!/usr/bin/env bash
 # Build the EJClaw reviewer container image
+# Runs from project root so Dockerfile can COPY runners/agent-runner/
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-cd "$SCRIPT_DIR"
+PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
 
 echo "Building ejclaw-reviewer container image..."
-docker build -t ejclaw-reviewer:latest .
+docker build -f "$SCRIPT_DIR/Dockerfile" -t ejclaw-reviewer:latest "$PROJECT_ROOT"
 echo "Done. Image: ejclaw-reviewer:latest"