Packaged windows claim `com.nousresearch.hermes` as their Wayland app id
(electron-builder bakes product-identity.cjs's `appId` into
extraMetadata.desktopName; Electron hands that string to the compositor
verbatim), while the entry was written as `hermes.desktop` with
`StartupWMClass=Hermes` — so GNOME matched neither StartupWMClass nor a
`<app_id>.desktop` file name and every launch fell back to the placeholder
icon, with the raw app id in the tooltip.
- write `<app_id>.desktop` with `StartupWMClass=<app_id>` (Name= stays "Hermes")
- retire a leftover `hermes.desktop` once the new entry is on disk, and only
when the file still names this app and launcher management is enabled;
foreign files at that path are left alone
- nix/desktop.nix derives the entry file name from the module instead of
hardcoding it
- tests: the installed entry carries the app id, legacy retirement, foreign-file
preservation, opt-out preservation, plus a node probe asserting
APP_ID == product-identity.cjs appId
Known consequence: an existing taskbar pin points at the old entry id and has to
be re-added once.