feat(research): one option per way to run a game, SteamCMD recommended

A draft built on a ready-made image whose files all live outside /server
went round three times and ended as WIP, although research had also
verified the game's Steam app, which SteamCMD installs straight into
/server. The build picked among the variant's images on its own.

- research reads each Steam app's OS list. When it ships a Linux server,
  the SteamCMD route is the recommended option; for Windows-only servers,
  images that bring Proton or Wine come first. The research prompt says
  the same.
- A variant that can run on several images becomes one option per image
  ("... (SteamCMD)", "... (image x/y)"), so the admin picks exactly how the
  server runs.
- build uses exactly the chosen option and never switches to another; if it
  can't be made to work, the PR says so and another option can be picked.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/gbrgames/research_test.go

@@ -39,3 +39,76 @@ func TestAppNameFromAppInfo(t *testing.T) {
 		t.Errorf("got %v", m)
 	}
 }
+
+func TestParseAppInfoFindsLinuxServers(t *testing.T) {
+	linux, ok := parseAppInfo(`"1000000"
+{
+	"common"
+	{
+		"name"		"Example Dedicated Server"
+		"oslist"		"windows,linux"
+	}
+}`)
+	if !ok || linux.name != "Example Dedicated Server" || !linux.linux {
+		t.Errorf("got %+v %v", linux, ok)
+	}
+	// A server that only exists for Windows (needs Proton or Wine)
+	windows, _ := parseAppInfo(`"common" { "name" "Example Server" "oslist" "windows" }`)
+	if windows.linux {
+		t.Error("windows-only app reported as linux")
+	}
+}
+
+func TestWithSteamCMDGoesFirstOnlyForLinuxServers(t *testing.T) {
+	images := []string{"someone/example-server", "cm2network/steamcmd", "other/example"}
+	got := withSteamCMD(images, true)
+	if len(got) != 3 || got[0] != "cm2network/steamcmd" || got[1] != "someone/example-server" {
+		t.Errorf("linux: %v", got)
+	}
+	got = withSteamCMD([]string{"someone/proton-example"}, false)
+	if len(got) != 2 || got[1] != "cm2network/steamcmd" {
+		t.Errorf("windows-only: %v", got)
+	}
+}
+
+func TestRecommendPrefersTheSteamCMDVariant(t *testing.T) {
+	v := []variant{
+		{ID: "image", Recommended: true, Images: []string{"someone/example-server"}},
+		{ID: "steam", Images: []string{"cm2network/steamcmd", "someone/example-server"}},
+		{ID: "broken", Recommended: true},
+	}
+	recommend(v)
+	if v[0].Recommended || !v[1].Recommended || v[2].Recommended {
+		t.Errorf("got %+v", v)
+	}
+	// Without a SteamCMD variant, the model's runnable choice stands
+	v = []variant{{ID: "a", Images: []string{"x/a"}}, {ID: "b", Recommended: true, Images: []string{"x/b"}}}
+	recommend(v)
+	if v[0].Recommended || !v[1].Recommended {
+		t.Errorf("got %+v", v)
+	}
+}
+
+func TestOneOptionPerImageThenSteamCMDRecommended(t *testing.T) {
+	v := oneOptionPerImage([]variant{{
+		ID: "dedicated", Title: "Example Dedicated Server", Recommended: true, SteamAppID: "1000000",
+		Images:   withSteamCMD([]string{"someone/example-server"}, true),
+		Verified: []string{"image someone/example-server exists", "Steam app 1000000 is \"Example Dedicated Server\""},
+	}})
+	recommend(v)
+	if len(v) != 2 {
+		t.Fatalf("want one option per image, got %+v", v)
+	}
+	steam, image := v[0], v[1]
+	if steam.Title != "Example Dedicated Server (SteamCMD)" || !steam.Recommended || steam.SteamAppID != "1000000" || len(steam.Images) != 1 {
+		t.Errorf("SteamCMD option: %+v", steam)
+	}
+	if image.Title != "Example Dedicated Server (image someone/example-server)" || image.Recommended || image.SteamAppID != "" {
+		t.Errorf("image option: %+v", image)
+	}
+	for _, line := range steam.Verified {
+		if line == "image someone/example-server exists" {
+			t.Error("SteamCMD option lists the other option's image check")
+		}
+	}
+}