refactor: remove deployment.json and use direct selectors

- Remove deployment.json file generation from outputs.nix
- Add throw for deprecated deployment.file usage with upgrade instructions
- Remove vars data from deployment.data
- Update Machine class to use direct select() calls instead of deployment property
- Update all deployment property accesses to use direct selectors
- Add precaching for frequently accessed values in update.py:
  - Module paths for facts and vars
  - Deployment settings (requireExplicitUpdate, nixosMobileWorkaround)
  - Services and generators data
  - Secret upload locations
- This removes unnecessary JSON serialization and makes the code more composable

nixosModules/clanCore/vars/default.nix

@@ -73,10 +73,5 @@ in
       ) [ ] (lib.attrValues generator.files)
     ) [ ] (lib.attrValues config.clan.core.vars.generators);
 
-    system.clan.deployment.data = {
-      vars = config.clan.core.vars._serialized;
-      inherit (config.clan.core.networking) targetHost buildHost;
-      inherit (config.clan.core.deployment) requireExplicitUpdate;
-    };
   };
 }