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/build.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/bash
+
+# Download the required library
+curl -L -o /app/libfdb_c.so https://github.com/apple/foundationdb/releases/download/${PACKAGE_VERSION}/libfdb_c.x86_64.so
+
+# Make the library readable
+chmod 755 /app/libfdb_c.so
+
+# Build the RPM
+nfpm pkg --config /app/resources/nfpm.yaml --target /app/dist --packager rpm