Add download --list-workloads/--list-components/--print-deps-tree, and CI

- download --list-workloads / --list-components print every workload or
  component id (with its manifest title) without downloading anything, for
  discovering what to pass as a package id or --with-* toggle.
- download --print-deps-tree prints the dependency tree of whatever the
  current flags would actually select, sharing the exact same
  arch/--ignore/Optional/Recommended filtering ExpandSelection uses so the
  output matches a real download; diamond dependencies are shown once and
  referenced as "(see above)" afterwards to keep it finite.
- Fixed --manifest (offline/predownloaded manifest testing) never having
  worked at all: it builds a "file:" URL but the shared http.Client had no
  handler registered for that scheme.
- Added a CI workflow running gofmt/vet/build/test on every push and PR;
  previously only the tag-triggered release workflow existed.

cmd/msvc-go-wine/download.go

@@ -30,6 +30,9 @@ func runDownload(args []string) int {
 	onlyUnpack := fs.Bool("only-unpack", false, "unpack selected packages and keep everything, without pruning to just the CLI tools")
 	keepUnpack := fs.Bool("keep-unpack", false, "keep the scratch unpack dir instead of removing it after moving files into place")
 	skipPatch := fs.Bool("skip-patch", false, "don't apply the Wine compatibility patches")
+	listWorkloads := fs.Bool("list-workloads", false, "list available workloads from the manifest and exit, without downloading anything")
+	listComponents := fs.Bool("list-components", false, "list available components from the manifest and exit, without downloading anything")
+	printDepsTree := fs.Bool("print-deps-tree", false, "print the dependency tree of the selected packages and exit, without downloading anything")
 	var archsFlag stringList
 	fs.Var(&archsFlag, "architecture", "target architecture to include (x86, x64, arm, arm64, host); repeatable")
 	var ignoreFlag stringList
@@ -78,7 +81,17 @@ func runDownload(args []string) int {
 
 	idx := download.BuildIndex(manifest, opts.HostArch, opts.Language)
 
-	if !*acceptLicense {
+	if *listWorkloads || *listComponents {
+		if *listWorkloads {
+			printPackageList("Workload", download.PackagesByType(idx, "Workload"), opts.Language)
+		}
+		if *listComponents {
+			printPackageList("Component", download.PackagesByType(idx, "Component"), opts.Language)
+		}
+		return 0
+	}
+
+	if !*acceptLicense && !*printDepsTree {
 		license := "the Visual Studio Build Tools license"
 		if p := idx.Find("Microsoft.VisualStudio.Product.BuildTools", nil); p != nil && len(p.LocalizedResources) > 0 {
 			license = p.LocalizedResources[0].License
@@ -93,6 +106,11 @@ func runDownload(args []string) int {
 		return 1
 	}
 
+	if *printDepsTree {
+		download.PrintDependencyTree(os.Stdout, idx, opts)
+		return 0
+	}
+
 	selected, err := download.ExpandSelection(idx, opts)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "msvc-go-wine download:", err)
@@ -184,6 +202,19 @@ func runDownload(args []string) int {
 	return 0
 }
 
+// printPackageList prints one line per package: its ID, and (when the
+// manifest carries one) its human-readable title in the requested language.
+func printPackageList(kind string, pkgs []*download.Package, language string) {
+	fmt.Printf("Available %ss (%d):\n", kind, len(pkgs))
+	for _, p := range pkgs {
+		if lr := p.Localized(language); lr != nil && lr.Title != "" {
+			fmt.Printf("  %-65s %s\n", p.ID, lr.Title)
+		} else {
+			fmt.Printf("  %s\n", p.ID)
+		}
+	}
+}
+
 func detectHostArch() string {
 	if runtime.GOARCH == "arm64" {
 		return "arm64"