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/stalwart-cli/resources/nfpm.yaml

@@ -0,0 +1,31 @@
+# nfpm.yaml
+
+name: stalwart-cli
+version: ${PACKAGE_VERSION}
+release: ${PACKAGE_RELEASE}
+arch: amd64
+platform: linux
+section: default
+priority: extra
+description: "Stalwart CLI - Command line interface for Stalwart Mail Server"
+
+maintainer: Stalwart Labs
+homepage: https://stalw.art
+license: AGPL-3.0
+
+disable_globbing: false
+
+replaces:
+  - stalwart-cli
+
+provides:
+  - stalwart-cli
+
+# Files to include in the package
+contents:
+  - src: /app/stalwart-cli
+    dst: /usr/bin/stalwart-cli
+    file_info:
+      mode: 0755
+      owner: root
+      group: root