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-remove-preinstalls

@@ -24,6 +24,12 @@ if gum confirm "Are you sure you want to remove all preinstalled web apps, TUI w
     rm -f ~/.local/bin/cursor-agent
   fi
 
+  # Preserve a user-managed Muse launcher at the same path.
+  if [[ -f ~/.local/bin/muse && ! -L ~/.local/bin/muse ]] &&
+    grep -Eq '^mise use -g .*"http:muse\[' ~/.local/bin/muse; then
+    rm -f ~/.local/bin/muse
+  fi
+
   # Only the wrapper omarchy-install-hermes-cli wrote is a preinstall. Hermes
   # Desktop's command, an official install, or anything else at that path is
   # the user's, so it is the installer that decides whether the wrapper is its