feat(aur): rewrite with go-git, RPC batch queries, functional options

- Replace shell git clone with go-git for cloning/pulling PKGBUILDs
- Add rpcInfoMulti for batch AUR queries (single HTTP request)
- Add functional options: WithBuildDir, WithMakepkgFlags
- Implement proper remove/purge via pacman -R/-Rns
- Fix temp directory leak: buildPackage returns cleanup path
- Remove NameNormalizer (AUR names are plain identifiers)
- Update README capability matrix
- Remove duplicate platform stubs (flatpak, ports)

flatpak/flatpak_linux.go

@@ -198,49 +198,6 @@ func removeRepo(ctx context.Context, id string) error {
 	return err
 }
 
-func latestVersion(ctx context.Context, pkg string) (string, error) {
-	out, err := run(ctx, []string{"remote-info", "flathub", pkg})
-	if err != nil {
-		if strings.Contains(err.Error(), "exit status 1") {
-			return "", fmt.Errorf("flatpak latestVersion %s: %w", pkg, snack.ErrNotFound)
-		}
-		return "", fmt.Errorf("flatpak latestVersion: %w", err)
-	}
-	p := parseInfo(out)
-	if p == nil || p.Version == "" {
-		return "", fmt.Errorf("flatpak latestVersion %s: %w", pkg, snack.ErrNotFound)
-	}
-	return p.Version, nil
-}
-
-func listUpgrades(ctx context.Context) ([]snack.Package, error) {
-	out, err := run(ctx, []string{"remote-ls", "--updates", "--columns=name,application,version,origin"})
-	if err != nil {
-		if strings.Contains(err.Error(), "No updates") {
-			return nil, nil
-		}
-		return nil, fmt.Errorf("flatpak listUpgrades: %w", err)
-	}
-	return parseList(out), nil
-}
-
-func upgradeAvailable(ctx context.Context, pkg string) (bool, error) {
-	upgrades, err := listUpgrades(ctx)
-	if err != nil {
-		return false, err
-	}
-	for _, u := range upgrades {
-		if u.Name == pkg || u.Description == pkg {
-			return true, nil
-		}
-	}
-	return false, nil
-}
-
-func versionCmp(_ context.Context, ver1, ver2 string) (int, error) {
-	return semverCmp(ver1, ver2), nil
-}
-
 func upgradePackages(ctx context.Context, pkgs []snack.Target, opts ...snack.Option) (snack.InstallResult, error) {
 	o := snack.ApplyOptions(opts...)
 	var toUpgrade []snack.Target