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)

migrations/1788724825.sh

@@ -0,0 +1,5 @@
+echo "Install Muse Code via mise wrapper"
+
+if omarchy-cmd-missing muse && [[ ! -f $HOME/.local/state/omarchy/preinstalls-removed ]]; then
+  omarchy-mise-install "http:muse[url=https://api.meta.ai/muse-launcher.sh,bin=muse,version_list_url=https://api.meta.ai/muse-code/channels/muse-stable,version_json_path=.version]" muse
+fi