fix: auto-flatten single subfolder in uploaded ZIP files for build context

GitHub-downloaded ZIPs contain files inside a subfolder (e.g., repo-main/).
The build init container now detects this pattern and flattens the contents
to the workspace root so Kaniko can find package.json and other files.

backend/src/build/build.service.ts

@@ -137,9 +137,23 @@ export class BuildService {
         command: ['sh', '-c', `
           apk add --no-cache unzip &&
           cp /workspace/Dockerfile /workspace-out/Dockerfile &&
-          mkdir -p /workspace-out/source &&
-          cd /workspace-out/source &&
+          mkdir -p /tmp/extract &&
+          cd /tmp/extract &&
           unzip /source/source.zip &&
+          echo "--- Extracted contents ---" &&
+          ls -la /tmp/extract/ &&
+          mkdir -p /workspace-out/source &&
+          ITEMS=$(ls -1 /tmp/extract/ | head -5) &&
+          COUNT=$(ls -1 /tmp/extract/ | wc -l) &&
+          if [ "$COUNT" -eq 1 ] && [ -d "/tmp/extract/$ITEMS" ]; then
+            echo ">>> Single subfolder detected: $ITEMS — flattening to root" &&
+            cp -a /tmp/extract/$ITEMS/. /workspace-out/source/
+          else
+            echo ">>> Multiple items or files — copying as-is" &&
+            cp -a /tmp/extract/. /workspace-out/source/
+          fi &&
+          rm -rf /tmp/extract &&
+          echo "--- Final workspace contents ---" &&
           ls -la /workspace-out/source/
         `],
         volumeMounts: [