Fix cross-platform builds: process cleanup and disk space checking

- Add platform-specific implementations for Windows, BSD systems
- Create platform-specific disk space checking with proper syscalls
- Add Windows process cleanup using tasklist/taskkill
- Add BSD-specific Statfs_t field handling (F_blocks, F_bavail, F_bsize)
- Support 9/10 target platforms (Linux, Windows, macOS, FreeBSD, OpenBSD)
- Process cleanup now works on all Unix-like systems and Windows
- Phase 2 TUI improvements compatible across platforms

internal/cleanup/processes.go

@@ -1,3 +1,6 @@
+//go:build !windows
+// +build !windows
+
 package cleanup
 
 import (