feat: create shared extraHosts module with Tailscale IPs

- Create modules/network/extraHosts.nix with Tailscale IP mappings
- Replace hardcoded networking.extraHosts in all machine configs
- Add extraHosts module import to all machines
- Enable Tailscale service by default in the module
- Use Tailscale mesh network IPs for reliable connectivity

machines/reverse-proxy/configuration.nix

@@ -4,6 +4,7 @@
   imports = [ 
     ./gandicloud.nix
     ../../modules/common/base.nix
+    ../../modules/network/extraHosts.nix
     ../../modules/users/sma.nix
     ../../modules/security/ssh-keys.nix
   ];