Add regression test for hasGmailSource filtering

Covers three cases: no sources (hint shown), non-Gmail source only
(hint shown), and Gmail source exists (hint suppressed). This logic
regressed across multiple commits so it deserves explicit coverage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wesm

cmd/msgvault/cmd/addaccount_test.go

@@ -0,0 +1,42 @@
+package cmd
+
+import (
+	"testing"
+
+	"github.com/wesm/msgvault/internal/store"
+)
+
+func TestHasGmailSource(t *testing.T) {
+	tmpDir := t.TempDir()
+	s, err := store.Open(tmpDir + "/msgvault.db")
+	if err != nil {
+		t.Fatalf("open store: %v", err)
+	}
+	defer func() { _ = s.Close() }()
+	if err := s.InitSchema(); err != nil {
+		t.Fatalf("init schema: %v", err)
+	}
+
+	const email = "user@company.com"
+
+	// No sources at all — should suggest add-account.
+	if hasGmailSource(s, email) {
+		t.Error("hasGmailSource should be false with no sources")
+	}
+
+	// Non-Gmail source exists — should still suggest add-account.
+	if _, err := s.GetOrCreateSource("mbox", email); err != nil {
+		t.Fatalf("create mbox source: %v", err)
+	}
+	if hasGmailSource(s, email) {
+		t.Error("hasGmailSource should be false with only mbox source")
+	}
+
+	// Gmail source exists — should suppress the hint.
+	if _, err := s.GetOrCreateSource("gmail", email); err != nil {
+		t.Fatalf("create gmail source: %v", err)
+	}
+	if !hasGmailSource(s, email) {
+		t.Error("hasGmailSource should be true with gmail source")
+	}
+}