refactor: systemd units in services/, read with service_file like patches/

services/README.md

@@ -0,0 +1,16 @@
+# Services
+
+The systemd units Steamify installs, kept out of the shell code so they can
+be read and reviewed on their own. `lib/*.sh` reads them with `service_file
+<name> [KEY=value...]`, which fills in `@KEY@` placeholders (paths the
+scripts define); the single-file build (`.github/tools/bundle.sh`) embeds
+them. Small drop-ins that only add a line or two to someone else's unit stay
+in the shell code.
+
+| File | Used by | What |
+|---|---|---|
+| `steamify-boot-desktop.service` | `lib/boot-session.sh` (Boot into: desktop) | Sets the Plasma session before the login manager starts |
+| `sync-steamos-session.path`, `.service` | `lib/login-manager.sh` (SteamOS conversion, plasma-login-manager) | The sync bridge: copies Steam's session choice into `plasmalogin.conf` |
+| `steam-desktop-autostart.service` | `lib/steam-desktop.sh` (SteamOS conversion) | Steam in the background on the Plasma desktop (user unit) |
+| `ensure-kernel-headers.service` | `lib/steam-machine.sh` (Steam Machine support) | Installs missing kernel headers at boot, so DKMS builds for every kernel |
+| `steamify-update-check.service`, `.timer` | `lib/update-notifier.sh` (Update notifications) | The daily and login check for a new release (user units) |