fix: FQDN resolution and display_name blank bug; fix: Arch/Alpine/RPM packages

Bug fixes:
- get_fqdn() now prioritizes 'hostname -f' (returns full FQDN) over /etc/hostname (returns short hostname)
- Added get_hostname() for short hostname extraction
- Added hostname field to EnrollmentRequest for manager display_name population
- Updated SPEC.md and API_DOCUMENTATION.md

Package fixes:
- Arch: Added linux-patch-api.install with post_install/upgrade/remove hooks, user creation, directory creation, config handling
- Alpine: Added linux-patch-api.apk-install with pre/post install/deinstall hooks, user creation, directory creation, config handling, missing config.yaml.example
- RPM: Dynamic version from Cargo.toml, %ghost %config(noreplace) for live configs, tarball exclusions, /var/log in %files

tests/integration/enrollment_test.rs

@@ -473,6 +473,18 @@ async fn test_registration_payload_structure() {
         os_obj.contains_key("distro") || os_obj.contains_key("kernel"),
         "os_details should contain distro or kernel information"
     );
+
+    // Verify hostname field (optional, may be present or absent)
+    // When present, it should be a non-empty string without dots (short hostname)
+    if let Some(hostname) = payload.get("hostname").and_then(|v| v.as_str()) {
+        assert!(!hostname.is_empty(), "hostname should not be empty when present");
+        assert!(
+            !hostname.contains('.'),
+            "hostname should be short form (no dots), got: {}",
+            hostname
+        );
+    }
+    // hostname field is optional — its absence is valid (skip_serializing_if = None)
 }
 
 // =============================================================================