Restructure modules/shared and update all imports

- Rename modules/hosts/common to modules/shared
- Split shared into home/general, home/linux, and nixos subdirectories
- Update all import paths in lib/ and modules/hosts/
- Fix hardcoded /Users/ path to use config.home.homeDirectory
- Update .sops.yaml path for secrets

modules/shared/home/linux/apps/hexchat.nix

@@ -0,0 +1,3 @@
+{ ... }: {
+  programs.hexchat.enable = true;
+}