Add Muse Code as a default coding agent (#9915)

* Add Muse Code as a default coding agent

Meta ships Muse Code only as a binary, so it installs from the AUR
(muse-code-bin) instead of mise, and a fresh install runs the muse login
browser flow in the install terminal before the agent opens.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0148qKzr366p2Ubu2igCLvPg

* Refine Muse Code menu and prompt forwarding

* Install Muse Code from OPR

* Install Muse Code through mise's HTTP backend

* Preinstall the Muse mise stub

* Use the shared Muse installation flow

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: David Heinemeier Hansson <david@hey.com>
(cherry picked from commit 0d223fe820)

bin/omarchy-agent

@@ -110,6 +110,11 @@ hermes)
     command=(hermes --yolo)
   fi
   ;;
+muse)
+  # --approval-mode never skips the tool prompts but keeps Muse's own sandbox.
+  command=(muse --approval-mode never)
+  [[ -n ${prompt:-} ]] && command+=(-- "$prompt")
+  ;;
 omp)
   command=(omp --auto-approve)
   [[ -n ${prompt:-} ]] && command+=(-- "$prompt")