Add Dim Agent CLI to the agent roster and Install > AI

npm dimcode (bin: dim) rides the mise path like Deep Code; entries
land alphabetically in the Default Agent and Install > AI menus.
CLI-only per dimagent.cn, login handled by the CLI itself.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QKxGW1raAWaqeU8WdHsMsp

bin/omarchy-agent

@@ -107,6 +107,10 @@ deepcode)
   command=(deepcode)
   [[ -n ${prompt:-} ]] && command+=("$prompt")
   ;;
+dim)
+  command=(dim)
+  [[ -n ${prompt:-} ]] && command+=("$prompt")
+  ;;
 *)
   echo "Unsupported default agent: $agent" >&2
   exit 1