fix: add cross-platform disk detection for Windows/macOS builds

- Split detectDiskSpace() into platform-specific files with build tags
- disk_unix.go: Uses unix.Statfs for Linux and macOS
- disk_windows.go: Uses windows.GetDiskFreeSpaceEx for Windows
- Fixes Windows cross-compilation build errors

🤖 Generated with Claude Code

internal/pkg/envcheck/capabilities.go

@@ -14,7 +14,6 @@ import (
 	"time"
 
 	"github.com/docker/docker/client"
-	"golang.org/x/sys/unix"
 )
 
 // DiskInfo holds disk space information
@@ -164,33 +163,6 @@ func generateSuggestedLabels(cap *RunnerCapabilities) []string {
 	return labels
 }
 
-// detectDiskSpace detects disk space on the root filesystem
-func detectDiskSpace() *DiskInfo {
-	var stat unix.Statfs_t
-
-	// Get stats for root filesystem (or current working directory)
-	path := "/"
-	if runtime.GOOS == "windows" {
-		path = "C:\\"
-	}
-
-	err := unix.Statfs(path, &stat)
-	if err != nil {
-		return nil
-	}
-
-	total := stat.Blocks * uint64(stat.Bsize)
-	free := stat.Bavail * uint64(stat.Bsize)
-	used := total - free
-	usedPercent := float64(used) / float64(total) * 100
-
-	return &DiskInfo{
-		Total:       total,
-		Free:        free,
-		Used:        used,
-		UsedPercent: usedPercent,
-	}
-}
 
 // ToJSON converts capabilities to JSON string for transmission
 func (c *RunnerCapabilities) ToJSON() string {

internal/pkg/envcheck/disk_unix.go

@@ -0,0 +1,32 @@
+//go:build unix
+
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package envcheck
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// detectDiskSpace detects disk space on the root filesystem (Unix version)
+func detectDiskSpace() *DiskInfo {
+	var stat unix.Statfs_t
+
+	err := unix.Statfs("/", &stat)
+	if err != nil {
+		return nil
+	}
+
+	total := stat.Blocks * uint64(stat.Bsize)
+	free := stat.Bavail * uint64(stat.Bsize)
+	used := total - free
+	usedPercent := float64(used) / float64(total) * 100
+
+	return &DiskInfo{
+		Total:       total,
+		Free:        free,
+		Used:        used,
+		UsedPercent: usedPercent,
+	}
+}

internal/pkg/envcheck/disk_windows.go

@@ -0,0 +1,31 @@
+//go:build windows
+
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package envcheck
+
+import (
+	"golang.org/x/sys/windows"
+)
+
+// detectDiskSpace detects disk space on the C: drive (Windows version)
+func detectDiskSpace() *DiskInfo {
+	var freeBytesAvailable, totalNumberOfBytes, totalNumberOfFreeBytes uint64
+
+	path := windows.StringToUTF16Ptr("C:\\")
+	err := windows.GetDiskFreeSpaceEx(path, &freeBytesAvailable, &totalNumberOfBytes, &totalNumberOfFreeBytes)
+	if err != nil {
+		return nil
+	}
+
+	used := totalNumberOfBytes - totalNumberOfFreeBytes
+	usedPercent := float64(used) / float64(totalNumberOfBytes) * 100
+
+	return &DiskInfo{
+		Total:       totalNumberOfBytes,
+		Free:        totalNumberOfFreeBytes,
+		Used:        used,
+		UsedPercent: usedPercent,
+	}
+}