fix: preserve abuild directory structure in Alpine cleanup

- Replace aggressive rm -rf /home/builduser/packages/ with targeted rm -f of stale .apk files
- Add mkdir -p to ensure abuild output directory exists before build
- Fixes Alpine CI build failure caused by removing required directory structure

build-alpine.sh

@@ -10,8 +10,9 @@ echo ""
 
 # Clean stale packages from previous builds
 rm -f releases/linux-patch-api-*.apk 2>/dev/null || true
-rm -rf /home/builduser/packages/home/x86_64/ 2>/dev/null || true
-rm -rf /home/builduser/packages/ 2>/dev/null || true
+rm -f /home/builduser/packages/home/x86_64/linux-patch-api-*.apk 2>/dev/null || true
+# Ensure abuild output directory exists
+mkdir -p /home/builduser/packages/home/x86_64/
 
 # Source cargo environment (for rustup-installed toolchain in CI)
 if [ -f "$HOME/.cargo/env" ]; then