Restructure modules/shared and update all imports

- Delete 2024-12-rework/ folder
- Rename modules/hosts/common to modules/shared, then split into:
  - modules/shared/home/general
  - modules/shared/home/linux
  - modules/shared/nixos
- Update all import paths throughout the codebase
- Update lib/*.nix to use new paths
- Fix hardcoded /Users/${username} to use config.home.homeDirectory
- Update README and examples/flake-structure.nix

modules/hosts/nixos/kiosk-entryway/default.nix

@@ -97,7 +97,7 @@
         path = "${config.users.users.${username}.home}/.private-env";
       };
       wifi_creds = {
-        sopsFile = ../../common/secrets.yaml;
+        sopsFile = ../../../shared/secrets.yaml;
         restartUnits = [
           "wpa_supplicant.service"
         ];

modules/hosts/nixos/kiosk-entryway/monitoring.nix

@@ -120,7 +120,7 @@ in {
       vmagent_push_pw = {
         owner = "vmagent";
         restartUnits = ["vmagent.service"];
-        sopsFile = ../../../common/secrets.yaml;
+        sopsFile = ../../../../shared/secrets.yaml;
       };
     };
   };