Clean stale mounts before agent rootfs build

Unmount and remove leftover files from previous failed install
attempts before starting the agent rootfs build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/install.sh

@@ -262,6 +262,11 @@ if [[ -f "$FIRECLAW_DIR/agent-rootfs.ext4" ]]; then
     skip "Agent rootfs"
 else
     log "Creating 1G agent rootfs from Alpine base..."
+    # Clean up any stale mounts from previous failed runs
+    sudo umount /tmp/agent-build-mnt 2>/dev/null || true
+    sudo umount /tmp/fireclaw-alpine 2>/dev/null || true
+    rm -rf /tmp/agent-build-mnt /tmp/agent-build.ext4 2>/dev/null || true
+
     cp "$FIRECLAW_DIR/base-rootfs.ext4" /tmp/agent-build.ext4
     truncate -s 1G /tmp/agent-build.ext4