feat(winget): add Windows Package Manager support

Implements the full snack.Manager interface for winget:
- Install/Remove/Purge/Upgrade via winget CLI
- Search/List/Info/IsInstalled/Version queries
- Source (repository) management via RepoManager
- Version querying via VersionQuerier
- Targeted package upgrades via PackageUpgrader
- Name normalization via NameNormalizer

All commands use --disable-interactivity, --accept-source-agreements,
and --accept-package-agreements for non-interactive operation.

Parser handles winget's fixed-width tabular output by detecting column
positions from the header/separator lines. Includes VT100 escape
sequence stripping and progress line filtering.

Windows-only via build tags; other platforms return
ErrUnsupportedPlatform. Registered in detect_windows.go as the
default Windows package manager.

winget/capabilities.go

@@ -0,0 +1,49 @@
+package winget
+
+import (
+	"context"
+
+	"github.com/gogrlx/snack"
+)
+
+// Compile-time interface checks.
+var (
+	_ snack.VersionQuerier = (*Winget)(nil)
+	_ snack.RepoManager    = (*Winget)(nil)
+	_ snack.NameNormalizer = (*Winget)(nil)
+)
+
+// LatestVersion returns the latest available version of a package.
+func (w *Winget) LatestVersion(ctx context.Context, pkg string) (string, error) {
+	return latestVersion(ctx, pkg)
+}
+
+// ListUpgrades returns packages that have newer versions available.
+func (w *Winget) ListUpgrades(ctx context.Context) ([]snack.Package, error) {
+	return listUpgrades(ctx)
+}
+
+// UpgradeAvailable reports whether a newer version is available.
+func (w *Winget) UpgradeAvailable(ctx context.Context, pkg string) (bool, error) {
+	return upgradeAvailable(ctx, pkg)
+}
+
+// VersionCmp compares two version strings.
+func (w *Winget) VersionCmp(ctx context.Context, ver1, ver2 string) (int, error) {
+	return versionCmp(ctx, ver1, ver2)
+}
+
+// ListRepos returns configured winget sources.
+func (w *Winget) ListRepos(ctx context.Context) ([]snack.Repository, error) {
+	return sourceList(ctx)
+}
+
+// AddRepo adds a new winget source.
+func (w *Winget) AddRepo(ctx context.Context, repo snack.Repository) error {
+	return sourceAdd(ctx, repo)
+}
+
+// RemoveRepo removes a configured winget source.
+func (w *Winget) RemoveRepo(ctx context.Context, id string) error {
+	return sourceRemove(ctx, id)
+}