Add Migadu domain admin with shared lists, compaction, and safer apply.

Build the Go API and React UI for managing domain denylist/allowlist/recipient
deny and spam settings, plus shared lists that import/apply across domains with
wildcard compaction, entry verification, and Migadu-friendly list encoding
(including per-domain recipient filtering and rejection bisect on apply).

.gitignore

@@ -0,0 +1,24 @@
+# Binaries / local data
+/bin/
+/data/
+*.db
+*.exe
+/migaduadmin
+/tmp/
+
+# Env
+.env
+.env.local
+
+# Frontend
+web/node_modules/
+web/dist/
+
+# Editor / OS
+.DS_Store
+.idea/
+.vscode/
+*.swp
+
+# Go
+vendor/