refactor: use gopsutil and go-humanize for preflight checks

- Added gopsutil/v3 for cross-platform system metrics
  * Works on Linux, macOS, Windows, BSD
  * Memory detection no longer requires /proc parsing

- Added go-humanize for readable output
  * humanize.Bytes() for memory sizes
  * humanize.Comma() for large numbers

- Improved preflight display with memory usage percentage
- Linux kernel checks (shmmax/shmall) still use /proc for accuracy

go.mod

@@ -60,6 +60,7 @@ require (
 	github.com/charmbracelet/x/term v0.2.1 // indirect
 	github.com/cncf/xds/go v0.0.0-20250501225837-2ac532fd4443 // indirect
 	github.com/creack/pty v1.1.17 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/envoyproxy/go-control-plane/envoy v1.32.4 // indirect
 	github.com/envoyproxy/protoc-gen-validate v1.2.1 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
@@ -85,6 +86,7 @@ require (
 	github.com/muesli/termenv v0.16.0 // indirect
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/shirou/gopsutil/v3 v3.24.5 // indirect
 	github.com/spiffe/go-spiffe/v2 v2.5.0 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	github.com/zeebo/errs v1.4.0 // indirect