debug: add comprehensive directory listings to diagnose build conflicts

Add ls -la output for:
- Working directory before/after build
- Go build cache location and contents
- Go module cache contents
- Post-build state verification

Simple directory listings often reveal file permission issues,
cached artifacts, or leftover files that cause 'File exists' errors
better than complex debugging output.

.github/workflows/release.yml

@@ -138,6 +138,14 @@ jobs:
           echo "Files before build:"
           ls -la
 
+          # Debug: Show Go cache and module cache
+          echo "Go build cache location: $(go env GOCACHE)"
+          echo "Go module cache location: $(go env GOMODCACHE)"
+          echo "Go build cache contents:"
+          ls -la "$(go env GOCACHE)" 2>/dev/null || echo "Cache directory not accessible"
+          echo "Go module cache contents (top level):"
+          ls -la "$(go env GOMODCACHE)" 2>/dev/null || echo "Module cache directory not accessible"
+
           # Ensure clean build environment
           rm -f "$OUTPUT_NAME" "$OUTPUT_NAME.sha256" "$OUTPUT_NAME.sha512"
           go clean -cache
@@ -153,6 +161,10 @@ jobs:
             exit 1
           fi
 
+          # Debug: Show post-build state
+          echo "Files after successful build:"
+          ls -la
+
           # Verify binary was created and is executable
           ls -la "$OUTPUT_NAME"
           file "$OUTPUT_NAME"