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

lib/mkDarwinHost.nix

@@ -26,8 +26,8 @@
           useUserPackages = true;
           users.${username}.imports = [
             inputs.sops-nix.homeManagerModule # user-level secrets management
-            ../modules/hosts/common
-            ../modules/hosts/common/all-gui.nix
+            ../modules/shared/home/general
+            ../modules/shared/home/general/all-gui.nix
             ../modules/hosts/darwin/home.nix
             ../modules/hosts/darwin/${hostname}/home-${username}.nix 
           ];

lib/mkHomeConfig.nix

@@ -12,7 +12,7 @@
     # the path to your home.nix.
     modules = [
       ./nixpkgs-settings.nix
-      ../modules/hosts/common
+      ../modules/shared/home/general
       ../modules/hosts/home-manager-only
       ../modules/hosts/home-manager-only/home-${username}.nix
 

lib/mkNixosHost.nix

@@ -19,8 +19,8 @@
           useGlobalPkgs = true;
           useUserPackages = true;
           users.${username}.imports = [
-            ../modules/hosts/common
-            ../modules/hosts/common/linux/home.nix
+            ../modules/shared/home/general
+            ../modules/shared/home/linux
             ../modules/hosts/nixos/${hostname}/home-${username}.nix
           ];
         };