feat(Greeter): add auto-login feature for startup settings

- Introduced a new cli flag:
`dms greeter sync --autologin-only`
and updated UI toggle in Greeter settings

core/internal/greeter/installer_test.go

@@ -3,6 +3,7 @@ package greeter
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -96,3 +97,147 @@ func TestResolveGreeterThemeSyncState(t *testing.T) {
 		})
 	}
 }
+
+func TestUpsertInitialSession(t *testing.T) {
+	t.Parallel()
+
+	baseConfig := `[terminal]
+vt = 1
+
+[default_session]
+user = "greeter"
+command = "/usr/bin/dms-greeter --command niri"
+`
+
+	t.Run("inserts initial session", func(t *testing.T) {
+		t.Parallel()
+		got := upsertInitialSession(baseConfig, "alice", "niri", true)
+		if !strings.Contains(got, "[initial_session]") {
+			t.Fatalf("expected [initial_session] section, got:\n%s", got)
+		}
+		if !strings.Contains(got, `user = "alice"`) {
+			t.Fatalf("expected alice user in initial session, got:\n%s", got)
+		}
+		if !strings.Contains(got, `env XDG_SESSION_TYPE=wayland sh -c 'exec niri'`) {
+			t.Fatalf("expected wrapped session command, got:\n%s", got)
+		}
+	})
+
+	t.Run("updates existing initial session", func(t *testing.T) {
+		t.Parallel()
+		existing := baseConfig + `
+[initial_session]
+user = "bob"
+command = "old-command"
+`
+		got := upsertInitialSession(existing, "alice", "Hyprland", true)
+		if strings.Contains(got, `user = "bob"`) {
+			t.Fatalf("expected bob to be replaced, got:\n%s", got)
+		}
+		if !strings.Contains(got, `exec Hyprland`) {
+			t.Fatalf("expected Hyprland command, got:\n%s", got)
+		}
+	})
+
+	t.Run("removes initial session when disabled", func(t *testing.T) {
+		t.Parallel()
+		existing := baseConfig + `
+[initial_session]
+user = "alice"
+command = "niri"
+`
+		got := upsertInitialSession(existing, "", "", false)
+		if strings.Contains(got, "[initial_session]") {
+			t.Fatalf("expected initial session removed, got:\n%s", got)
+		}
+		if !strings.Contains(got, "[default_session]") {
+			t.Fatalf("expected default session preserved, got:\n%s", got)
+		}
+	})
+}
+
+func TestStripDesktopExecCodes(t *testing.T) {
+	t.Parallel()
+
+	got := stripDesktopExecCodes("niri --session %f")
+	want := "niri --session"
+	if got != want {
+		t.Fatalf("stripDesktopExecCodes = %q, want %q", got, want)
+	}
+}
+
+func TestResolveGreeterAutoLoginState(t *testing.T) {
+	t.Parallel()
+
+	cacheDir := t.TempDir()
+	homeDir := t.TempDir()
+
+	writeTestFile(t, filepath.Join(cacheDir, "settings.json"), `{
+  "greeterAutoLogin": true,
+  "greeterRememberLastUser": true,
+  "greeterRememberLastSession": true
+}`)
+	writeTestFile(t, filepath.Join(cacheDir, ".local/state/memory.json"), `{
+  "lastSuccessfulUser": "alice",
+  "lastSessionExec": "niri"
+}`)
+
+	enabled, loginUser, sessionExec, err := resolveGreeterAutoLoginState(cacheDir, homeDir)
+	if err != nil {
+		t.Fatalf("resolveGreeterAutoLoginState returned error: %v", err)
+	}
+	if !enabled || loginUser != "alice" || sessionExec != "niri" {
+		t.Fatalf("got enabled=%v user=%q exec=%q", enabled, loginUser, sessionExec)
+	}
+}
+
+func TestResolveGreeterAutoLoginStateIgnoresMemoryFlag(t *testing.T) {
+	t.Parallel()
+
+	cacheDir := t.TempDir()
+	homeDir := t.TempDir()
+
+	writeTestFile(t, filepath.Join(cacheDir, "settings.json"), `{
+  "greeterAutoLogin": false,
+  "greeterRememberLastUser": true,
+  "greeterRememberLastSession": true
+}`)
+	writeTestFile(t, filepath.Join(cacheDir, ".local/state/memory.json"), `{
+  "autoLoginEnabled": true,
+  "lastSuccessfulUser": "alice",
+  "lastSessionExec": "niri"
+}`)
+
+	enabled, loginUser, sessionExec, err := resolveGreeterAutoLoginState(cacheDir, homeDir)
+	if err != nil {
+		t.Fatalf("resolveGreeterAutoLoginState returned error: %v", err)
+	}
+	if enabled || loginUser != "" || sessionExec != "" {
+		t.Fatalf("expected disabled with empty user/exec, got enabled=%v user=%q exec=%q", enabled, loginUser, sessionExec)
+	}
+}
+
+func TestClearGreeterAutoLoginMemory(t *testing.T) {
+	t.Parallel()
+
+	memoryPath := filepath.Join(t.TempDir(), "memory.json")
+	writeTestFile(t, memoryPath, `{
+  "autoLoginEnabled": true,
+  "lastSuccessfulUser": "alice"
+}`)
+
+	if err := clearGreeterAutoLoginMemory(memoryPath, ""); err != nil {
+		t.Fatalf("clearGreeterAutoLoginMemory returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(memoryPath)
+	if err != nil {
+		t.Fatalf("failed to read memory file: %v", err)
+	}
+	if strings.Contains(string(data), "autoLoginEnabled") {
+		t.Fatalf("expected autoLoginEnabled removed, got: %s", string(data))
+	}
+	if !strings.Contains(string(data), "lastSuccessfulUser") {
+		t.Fatalf("expected other memory fields preserved, got: %s", string(data))
+	}
+}