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)

install/user/mise.sh

@@ -23,3 +23,6 @@ omarchy-mise-install aqua:modem-dev/hunk hunk
 # omarchy-provision-user -- the default browser, the mailto handler and the
 # finalize-user marker all come after it.
 omarchy-install-hermes-cli || true
+if omarchy-cmd-missing muse; 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