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/shared/nixos/flatpaks.nix

@@ -0,0 +1,20 @@
+
+{ ... }: {
+  services = {
+    flatpak = {
+      enable = true;
+      packages = [
+        "im.riot.Riot"
+        "com.cassidyjames.butler"
+        "com.logseq.Logseq"
+        "com.vivaldi.Vivaldi"
+        "org.signal.Signal"
+        "org.telegram.desktop"
+      ];
+      update.auto = {
+        enable = true;
+        onCalendar = "daily";
+      };
+    };
+  };
+}