Exclude password-protected pastes from public listings (#65)

ListPublic and its COUNT query now filter password_hash IS NULL, so
/api/public (and any page backed by it) no longer leaks metadata
(title, slug, existence) of password-protected pastes. Unlisted
pastes were already excluded. Adds regression test covering both.

internal/api/main_test.go

@@ -175,6 +175,46 @@ func TestListPublicExcludesUnlisted(t *testing.T) {
 	}
 }
 
+func TestListPublicExcludesPasswordAndUnlisted(t *testing.T) {
+	s := testServer(t)
+	h := s.routes()
+
+	bodies := []string{
+		`{"content":"open","visibility":"public"}`,
+		`{"content":"locked","visibility":"public","password":"hunter2"}`,
+		`{"content":"hidden","visibility":"unlisted"}`,
+	}
+	for _, body := range bodies {
+		req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		if rec.Code != 201 {
+			t.Fatalf("create %s: got %d", body, rec.Code)
+		}
+	}
+
+	req := httptest.NewRequest("GET", "/api/public", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != 200 {
+		t.Fatalf("list public: got %d", rec.Code)
+	}
+	var resp struct {
+		Total int              `json:"total"`
+		Items []map[string]any `json:"items"`
+	}
+	json.Unmarshal(rec.Body.Bytes(), &resp)
+	if resp.Total != 1 || len(resp.Items) != 1 {
+		t.Fatalf("expected only the 1 public paste, got total=%d items=%d", resp.Total, len(resp.Items))
+	}
+	// password-protected and unlisted pastes must not appear (no metadata leak)
+	for _, secret := range []string{"hunter2", "locked", "hidden"} {
+		if strings.Contains(rec.Body.String(), secret) {
+			t.Fatalf("leaked %q in /api/public response", secret)
+		}
+	}
+}
+
 func TestSweepSoftDeletesAfterGrace(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()