Add mosh for mobile shell access

- mosh package in systemPackages
- UDP ports 60000-60010 for mosh sessions

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

configuration.nix

@@ -85,6 +85,8 @@ in
     bsd-finger
     ytalk
     fortune
+    # Mobile shell - resilient SSH for spotty connections
+    mosh
     # Admin scripts (declarative deployment)
     dev-add
     dev-remove
@@ -134,6 +136,7 @@ in
   networking.firewall = {
     enable = true;
     allowedTCPPorts = [ 22 80 443 ];  # SSH, HTTP, HTTPS
+    allowedUDPPortRanges = [ { from = 60000; to = 60010; } ];  # mosh
 
     # Egress controls for regular users
     # UID range: 1000 (first regular user) to 65534 (nobody - excluded from controls)