feat(apt,dpkg): implement apt and dpkg package manager wrappers

Implement the snack.Manager interface for both apt (Debian/Ubuntu) and
dpkg (low-level Debian package tool).

apt wraps apt-get, apt-cache, and dpkg-query for full package management.
dpkg wraps dpkg and dpkg-query for low-level .deb operations.
Upgrade and Update return ErrUnsupportedPlatform for dpkg.

Both packages include:
- Linux implementations with proper error wrapping
- Non-linux build stubs returning ErrUnsupportedPlatform
- Output parsing helpers with tests
- Functional options support (sudo, assume-yes, dry-run)

dpkg/dpkg_linux.go

@@ -0,0 +1,138 @@
+//go:build linux
+
+package dpkg
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/gogrlx/snack"
+)
+
+func available() bool {
+	_, err := exec.LookPath("dpkg")
+	return err == nil
+}
+
+func install(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+	o := snack.ApplyOptions(opts...)
+	var args []string
+	if o.Sudo {
+		args = append(args, "sudo")
+	}
+	args = append(args, "dpkg", "-i")
+	if o.DryRun {
+		args = append(args, "--simulate")
+	}
+	args = append(args, pkgs...)
+	cmd := exec.CommandContext(ctx, args[0], args[1:]...)
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		errMsg := stderr.String()
+		if strings.Contains(errMsg, "Permission denied") || strings.Contains(errMsg, "are you root") {
+			return fmt.Errorf("dpkg -i: %w", snack.ErrPermissionDenied)
+		}
+		return fmt.Errorf("dpkg -i: %w: %s", err, errMsg)
+	}
+	return nil
+}
+
+func remove(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+	o := snack.ApplyOptions(opts...)
+	var args []string
+	if o.Sudo {
+		args = append(args, "sudo")
+	}
+	args = append(args, "dpkg", "-r")
+	if o.DryRun {
+		args = append(args, "--simulate")
+	}
+	args = append(args, pkgs...)
+	cmd := exec.CommandContext(ctx, args[0], args[1:]...)
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("dpkg -r: %w: %s", err, stderr.String())
+	}
+	return nil
+}
+
+func purge(ctx context.Context, pkgs []string, opts ...snack.Option) error {
+	o := snack.ApplyOptions(opts...)
+	var args []string
+	if o.Sudo {
+		args = append(args, "sudo")
+	}
+	args = append(args, "dpkg", "-P")
+	if o.DryRun {
+		args = append(args, "--simulate")
+	}
+	args = append(args, pkgs...)
+	cmd := exec.CommandContext(ctx, args[0], args[1:]...)
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("dpkg -P: %w: %s", err, stderr.String())
+	}
+	return nil
+}
+
+func list(ctx context.Context) ([]snack.Package, error) {
+	cmd := exec.CommandContext(ctx, "dpkg-query", "-W", "-f=${Package}\\t${Version}\\t${Status}\\n")
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("dpkg-query list: %w", err)
+	}
+	return parseList(string(out)), nil
+}
+
+func search(ctx context.Context, query string) ([]snack.Package, error) {
+	pattern := fmt.Sprintf("*%s*", query)
+	cmd := exec.CommandContext(ctx, "dpkg-query", "-l", pattern)
+	out, err := cmd.Output()
+	if err != nil {
+		// dpkg-query -l returns exit 1 when no packages match
+		return nil, nil
+	}
+	return parseDpkgList(string(out)), nil
+}
+
+func info(ctx context.Context, pkg string) (*snack.Package, error) {
+	cmd := exec.CommandContext(ctx, "dpkg-query", "-s", pkg)
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	out, err := cmd.Output()
+	if err != nil {
+		if strings.Contains(stderr.String(), "is not installed") || strings.Contains(stderr.String(), "not found") {
+			return nil, fmt.Errorf("dpkg-query -s %s: %w", pkg, snack.ErrNotInstalled)
+		}
+		return nil, fmt.Errorf("dpkg-query -s %s: %w", pkg, err)
+	}
+	return parseInfo(string(out))
+}
+
+func isInstalled(ctx context.Context, pkg string) (bool, error) {
+	cmd := exec.CommandContext(ctx, "dpkg-query", "-W", "-f=${Status}", pkg)
+	out, err := cmd.Output()
+	if err != nil {
+		return false, nil
+	}
+	return strings.TrimSpace(string(out)) == "install ok installed", nil
+}
+
+func version(ctx context.Context, pkg string) (string, error) {
+	cmd := exec.CommandContext(ctx, "dpkg-query", "-W", "-f=${Version}", pkg)
+	out, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("version %s: %w", pkg, snack.ErrNotInstalled)
+	}
+	v := strings.TrimSpace(string(out))
+	if v == "" {
+		return "", fmt.Errorf("version %s: %w", pkg, snack.ErrNotInstalled)
+	}
+	return v, nil
+}