port: rewrite bootstrap tool in Go

Replace the Python bootstrap script with a Go implementation that
cross-compiles to native binaries for Linux and macOS on x86_64 and
aarch64. The Go port preserves all sections of the original (system
packages, optional Flatpak GUI apps, custom downloads, and the macOS
firecracker VM bridge) and adds first-class pacman support so the tool
works on Arch-family distros alongside Debian, RHEL, and macOS.

A Makefile produces a host binary via `make build` and the full
four-target matrix under dist/ via `make build-all`.

check.go

@@ -0,0 +1,177 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+type systemCheckResult struct {
+	toInstallRegular []string
+	toInstallSpecial []string
+	alreadyInstalled []string
+	skipped          []string
+	remapped         []remap // for display only
+}
+
+type remap struct {
+	From string
+	To   []string
+}
+
+type flatpakCheckResult struct {
+	toInstall        []string
+	alreadyInstalled []string
+}
+
+type customCheckResult struct {
+	toInstall        []*CustomPackage
+	alreadyInstalled []customStatus
+}
+
+type customStatus struct {
+	pkg  *CustomPackage
+	path string
+}
+
+func checkSystemPackages(names []string) systemCheckResult {
+	overrides := packageOverrides[pkgMgr]
+	resolved, skipped := resolveSystemPkgs(names)
+
+	var remapped []remap
+	for _, n := range names {
+		if ov, ok := overrides[n]; ok && !ov.Skip {
+			remapped = append(remapped, remap{From: n, To: ov.Replacement})
+		}
+	}
+
+	specials := specialPkgs()
+	var special, regular []string
+	for _, p := range resolved {
+		if specials[p] {
+			special = append(special, p)
+		} else {
+			regular = append(regular, p)
+		}
+	}
+
+	var toR, alreadyR []string
+	for _, p := range regular {
+		if isSystemPkgInstalled(p) {
+			alreadyR = append(alreadyR, p)
+		} else {
+			toR = append(toR, p)
+		}
+	}
+	var toS, alreadyS []string
+	for _, p := range special {
+		if isSpecialPkgInstalled(p) {
+			alreadyS = append(alreadyS, p)
+		} else {
+			toS = append(toS, p)
+		}
+	}
+	return systemCheckResult{
+		toInstallRegular: toR,
+		toInstallSpecial: toS,
+		alreadyInstalled: append(alreadyR, alreadyS...),
+		skipped:          skipped,
+		remapped:         remapped,
+	}
+}
+
+func checkFlatpakPackages(ids []string) flatpakCheckResult {
+	var to, already []string
+	for _, p := range ids {
+		if isFlatpakInstalled(p) {
+			already = append(already, p)
+		} else {
+			to = append(to, p)
+		}
+	}
+	return flatpakCheckResult{toInstall: to, alreadyInstalled: already}
+}
+
+func checkCustomPackages(pkgs []*CustomPackage) customCheckResult {
+	var to []*CustomPackage
+	var already []customStatus
+	for _, p := range pkgs {
+		installed, path := isCustomPkgInstalled(p)
+		if installed {
+			already = append(already, customStatus{pkg: p, path: path})
+		} else {
+			to = append(to, p)
+		}
+	}
+	return customCheckResult{toInstall: to, alreadyInstalled: already}
+}
+
+func fmtList(items []string, limit int) string {
+	if len(items) <= limit {
+		return strings.Join(items, " ")
+	}
+	return strings.Join(items[:limit], " ") + fmt.Sprintf("  … +%d more", len(items)-limit)
+}
+
+func printCheckSummary(sys systemCheckResult, flat flatpakCheckResult, cust customCheckResult, only string) int {
+	total := 0
+
+	if only == "" || only == "system" {
+		toR := sys.toInstallRegular
+		toS := sys.toInstallSpecial
+		ok := sys.alreadyInstalled
+		fmt.Println("\nSystem packages:")
+		if len(ok) > 0 {
+			fmt.Printf("  [OK]      %3d already installed\n", len(ok))
+		}
+		n := len(toR) + len(toS)
+		if n > 0 {
+			combined := append([]string{}, toR...)
+			combined = append(combined, toS...)
+			fmt.Printf("  [INSTALL] %3d to install:  %s\n", n, fmtList(combined, 6))
+		}
+		if len(sys.skipped) > 0 {
+			fmt.Printf("  [SKIP]    %3d overridden (→ skip): %s\n", len(sys.skipped), fmtList(sys.skipped, 6))
+		}
+		if len(sys.remapped) > 0 {
+			var parts []string
+			for _, r := range sys.remapped {
+				parts = append(parts, fmt.Sprintf("%s→%s", r.From, strings.Join(r.To, ",")))
+			}
+			fmt.Printf("  [REMAP]       remapped: %s\n", strings.Join(parts, "  "))
+		}
+		total += n
+	}
+
+	if (only == "" || only == "flatpak") && (len(flat.toInstall) > 0 || len(flat.alreadyInstalled) > 0) {
+		fmt.Println("\nFlatpak packages:")
+		if len(flat.alreadyInstalled) > 0 {
+			fmt.Printf("  [OK]      %3d already installed\n", len(flat.alreadyInstalled))
+		}
+		if len(flat.toInstall) > 0 {
+			fmt.Printf("  [INSTALL] %3d to install:  %s\n", len(flat.toInstall), fmtList(flat.toInstall, 6))
+		}
+		total += len(flat.toInstall)
+	}
+
+	if only == "" || only == "custom" {
+		fmt.Println("\nCustom packages:")
+		for _, s := range cust.alreadyInstalled {
+			suffix := ""
+			if s.path != "" {
+				suffix = fmt.Sprintf("  (%s)", s.path)
+			}
+			fmt.Printf("  [OK]      %s%s\n", s.pkg.displayName(), suffix)
+		}
+		for _, p := range cust.toInstall {
+			_, path := isCustomPkgInstalled(p)
+			suffix := ""
+			if path != "" {
+				suffix = fmt.Sprintf("  → %s", path)
+			}
+			fmt.Printf("  [INSTALL] %s%s\n", p.displayName(), suffix)
+		}
+		total += len(cust.toInstall)
+	}
+
+	return total
+}