fix: keep SharePoint sync from blocking Home Manager activation

Preserve an in-flight timer job during service switching instead of restarting the oneshot and waiting for a potentially long synchronization. Herdr config installation succeeds; the activation timeout occurs later in reloadSystemd.

Verified the native keep-old behavior in pinned sources and a focused sd-switch dry run. Formatting, flake evaluation, Zenith build and whitespace checks passed. No live services changed; full activation remains user-controlled.

modules/capabilities/sharepoint-reference.nix

@@ -16,6 +16,8 @@
         Unit = {
           Description = "Refresh the local SharePoint reference mirror";
           ConditionPathExists = rcloneConfig;
+          # Let an in-flight sync finish; activation must not restart and wait for it.
+          X-SwitchMethod = "keep-old";
         };
 
         Service = {