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)

manual/17-ai.md

@@ -14,6 +14,7 @@ Omarchy treats AI coding agents as first-class citizens, but it doesn't pick a f
 | `pi`       | [Mario Zechner's Pi](https://github.com/badlogic/pi-mono)        |
 | `omp`      | [Oh My Pi](https://github.com/can1357/oh-my-pi)                  |
 | `hermes`   | [Hermes](https://hermes-agent.nousresearch.com/), Nous Research's agent  |
+| `muse`     | [Muse Code](https://dev.meta.ai), Meta's coding agent           |
 | `cursor-agent` | [Cursor CLI](https://cursor.com/cli)                         |
 
 To wrap an additional CLI the same way, run `omarchy-mise-install <package> [command-name]`. The stubs are kept current along with everything else mise manages when you run `omarchy update` (or the `mup` alias).
@@ -22,6 +23,8 @@ To wrap an additional CLI the same way, run `omarchy-mise-install <package> [com
 
 Pick your default agent with `omarchy default agent <name>` or under _Setup > Defaults > Agent_ in the Omarchy Menu (`Super + Space`). If the agent isn't installed yet, picking it installs it first. A fresh Omarchy will invite you to make this choice with a one-time notification.
 
+[Muse Code](https://dev.meta.ai) — Meta's `muse` — uses a preinstalled mise stub like the other agents. Picking it as the default installs Meta's official launcher through mise's HTTP backend. The launcher verifies and updates the native binary for your machine.
+
 Once you've chosen, `Super + Shift + Ctrl + A` launches the default agent in a dedicated terminal window (or brings up the picker if you haven't chosen yet). You can also launch it straight into a task with `omarchy agent prompt "Review this project"`. Agents launched this way run unattended in their respective don't-stop-to-ask modes, so be ready for them to actually do things! And since agents refuse to remember trust for your home directory, launches from `$HOME` start in `~/Work` instead.
 
 There are terminal shortcuts too: `a` runs the default agent inline in the current terminal, while `c`, `cx`, and `cy` start OpenCode, Claude Code, and Codex directly (again in their auto-approving modes). Theme changes sync to the agents as well: Claude Code, Pi, OpenCode, and Hermes (once Hermes Desktop is installed) all follow along when you switch the Omarchy theme.