feat(desktop/garmin-express): add Garmin Express via Wine

[fredclausen]

Summary

• Adds a new `desktop.garmin-express` module under `features/desktop/garmin-express/` that runs the Windows Garmin Express app in a dedicated Wine prefix, so map and firmware updates work for Garmin devices (e.g. Edge 840) on NixOS.
• Wired into `features/desktop/default.nix` and gated behind `desktop.enable_extra` (matches the pattern used by `ledger` / `trezor`).

Why

Garmin doesn't ship a Linux client. Native alternatives (manually copying `.img` files, Garmin Connect mobile) work for some cases but not for paid/preloaded TopoActive maps tied to Express. A reproducible Nix-managed Wine wrapper avoids the alternative of running a full Windows VM for one app.

How it works

The module:

• Pins the Garmin Express installer with `fetchurl` (sha256). Note: Garmin's URL is unversioned; the hash will need refreshing when they rotate the binary.
• Provides a `garmin-express` shell wrapper that, on first launch:
  1. Initialises a dedicated Wine prefix at `$XDG_DATA_HOME/wineprefixes/garmin-express`.
  2. Installs `corefonts` and `dotnet48` via `winetricks` (Express requires .NET Framework 4.x).
  3. Runs the Garmin Express installer interactively.
  4. Writes a `.garmin-express-installed` marker so subsequent launches skip setup.
• Launches `express.exe` (32-bit, under `Program Files (x86)`) with `--disable-gpu --disable-gpu-compositing` to work around CefSharp.Wpf rendering as a black window under XWayland.
• Adds a `.desktop` entry for app launchers.
• Adds a udev rule for Garmin USB vendor `091e` and enables `gvfs` for MTP support.
• Pulls in `wineWow64Packages.stable`, `winetricks`, `jmtpfs`, `libmtp`.

Caveats

• Reproducibility limits: the Wine prefix is mutable state on disk; only the installer hash and Wine version are Nix-pinned. `winetricks` also downloads .NET from Microsoft at runtime (cached in `~/.cache/winetricks`). This is the unavoidable trade-off for a closed-source vendor app.
• First-run is slow: ~10-20 minutes to install .NET 4.8 + Garmin Express. Subsequent launches are instant.
• GPU-accel disabled: required to avoid the black-window issue with CefSharp.Wpf under XWayland. Verified working on Hyprland.

Test plan

• Module evaluates (`nix-instantiate --parse`).
• Built successfully on `fredhub`.
• First-run setup completes (.NET 4.8 + Express installer).
• App launches and renders the UI with `--disable-gpu`.
• Edge 840 detected and map update flow tested end-to-end (next step on real hardware).

[Copilot]

Pull request overview

Adds an optional NixOS desktop module to install and run Garmin Express (Windows) under Wine with a dedicated per-user Wine prefix, integrated into the existing desktop.enable_extra feature-gating.

Changes:

• Introduces desktop.garmin-express module with a garmin-express wrapper that bootstraps a Wine prefix, installs prerequisites via winetricks, runs the pinned Garmin installer, and then launches Express with GPU disabled.
• Adds a .desktop entry and installs required MTP/Wine-related packages for configured users.
• Wires the module into features/desktop/default.nix and enables it when desktop.enable_extra is set.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
features/desktop/garmin-express/default.nix	New module that pins the installer, provides the Wine/winetricks bootstrap wrapper, and configures udev + packages needed for Garmin Express/MTP.
features/desktop/default.nix	Imports the new module and enables it behind desktop.enable_extra.

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