feat: add Stalwart Mail Server and FoundationDB library packages

- add stalwart: main mail server with systemd integration and user management
- add stalwart-cli: command line interface tool for server administration
- add stalwart-foundationdb: FoundationDB-enabled version with proper dependencies
- add libfoundationdb: FoundationDB client library (libfdb_c.so) package

All packages include proper conflict resolution, systemd services, and follow
repository packaging conventions. stalwart and stalwart-foundationdb are
mutually exclusive to prevent installation conflicts.

rpms/libfoundationdb/resources/scripts/postinstall.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+# Update the dynamic linker cache to include the new library
+ldconfig