blacklist: add domain reputation check via checker-blacklist

Integrates the checker-blacklist module behind a new POST /blacklist/domain
endpoint that aggregates reputation/blocklist sources for a given domain,
plus a SvelteKit UI under /blacklist/domain mirroring the existing IP
blacklist flow. Per-source credentials (VirusTotal, Safe Browsing) are
exposed as CLI flags; free sources run unconditionally.

Closes: #96

internal/config/blacklist.go

@@ -0,0 +1,40 @@
+// This file is part of the happyDeliver (R) project.
+// Copyright (c) 2025 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package config
+
+import (
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// AsCheckerOptions returns the map that checker-blacklist sources read
+// via stringOpt(). Empty values are omitted so sources that require a
+// credential stay disabled rather than failing with an empty key.
+func (b BlacklistConfig) AsCheckerOptions() sdk.CheckerOptions {
+	opts := sdk.CheckerOptions{}
+	if b.VirusTotalAPIKey != "" {
+		opts["virustotal_api_key"] = b.VirusTotalAPIKey
+	}
+	if b.SafeBrowsingAPIKey != "" {
+		opts["safebrowsing_api_key"] = b.SafeBrowsingAPIKey
+	}
+	return opts
+}