fix: Cross-platform build support (Windows, BSD, NetBSD)

Split resource limit checks into platform-specific files to handle
syscall API differences across operating systems.

Changes:
- Created resources_unix.go (Linux, macOS, FreeBSD, OpenBSD)
- Created resources_windows.go (Windows stub implementation)
- Created disk_check_netbsd.go (NetBSD stub - syscall.Statfs unavailable)
- Modified resources.go to delegate to checkPlatformLimits()
- Fixed BSD syscall.Rlimit int64/uint64 type conversions
- Made RLIMIT_AS check Linux-only (unavailable on OpenBSD)

Build Status:
✅ Linux (amd64, arm64, armv7)
✅ macOS (Intel, Apple Silicon)
✅ Windows (Intel, ARM)
✅ FreeBSD amd64
✅ OpenBSD amd64
✅ NetBSD amd64 (disk check returns safe defaults)

All 10/10 platforms building successfully.

internal/security/resources_windows.go

@@ -0,0 +1,27 @@
+// +build windows
+
+package security
+
+import (
+	"runtime"
+)
+
+// checkPlatformLimits returns resource limits for Windows
+func (rc *ResourceChecker) checkPlatformLimits() (*ResourceLimits, error) {
+	limits := &ResourceLimits{
+		Available: false, // Windows doesn't use Unix-style rlimits
+		Platform:  runtime.GOOS,
+	}
+
+	// Windows doesn't have the same resource limit concept
+	// Set reasonable defaults
+	limits.MaxOpenFiles = 8192 // Windows default is typically much higher
+	limits.MaxProcesses = 0    // Not applicable
+	limits.MaxAddressSpace = 0 // Not applicable
+
+	rc.log.Debug("Resource limits not available on Windows", "platform", "windows")
+
+	return limits, nil
+}
+
+