fix: keep MLX installed state independent of the chat demo

[joshuaswarren]

MLX should remain installed in the menu when its optional chat demo is removed. This change uses the capability reporter instead, with a migration that repairs existing installs without reinstalling their wheel or requiring the demo.

The matching installer is already published at joshuaswarren/mlx-omarchy@0545dc7. Both platform commands pin that commit and its verified checksum. The GPU label, menu icons, and installation prefix stay unchanged; this does not enable ANE execution.

All install-guard checks passed, including the real pinned-installer failure and failed-cleanup cases. A disposable-HOME smoke using a real installed wheel verified migration without the demo, repeated runs, an absent installation, missing-package failure, and preservation of an existing reporter. The generated launcher returns the native tool's same off-target backend error on this Linux x86 host. I have not run the graphical menu or a full M1 installation.

Evidence: https://github.com/joshuaswarren/mlx-omarchy/blob/0545dc7f8678c9d25800d37f96ab7262cb07fc2b/receipts/2026-09-12-durable-installed-state-key/receipt.md

[joshuaswarren]

The ARM job fails on two Neovim commands, not an MLX error. Both lack a command metadata summary:

Missing metadata summary: omarchy-nvim-refresh
Missing metadata summary: omarchy-nvim-setup
Command metadata check failed (2 issues)

The failed job reaches the final system checks. Both commands come from the pinned package source. I put that script and its symlink beside the base and PR versions of bin/omarchy. Both gave the same two errors. This ran omarchy commands --check, not the Neovim commands. The fix belongs in that package and its next build. I have not bypassed the check here.

The other three CI checks passed. Local QA passed all 10 MLX guard checks with no skips. The wider local suite has host-specific failures; its failure list matches the base branch exactly. Review found no blocking bugs. The real-wheel launcher checks passed in temporary homes. No live M1 install or graphical menu was tested.

A broken MLX install can still fail this migration and stop an update. It stays pending rather than getting a false success marker. The new menu key can hide removal until migration succeeds; users can still run omarchy-remove-ai-mlx directly. I kept that failure visible rather than mark a broken install as migrated.