feat: Add scripts and systemd services for SteamOS session management and game launching

ansible/files/game_station/bin/system/steamos-select-branch

@@ -0,0 +1,30 @@
+#!/bin/bash
+set -euo pipefail
+LOGFILE="$HOME/.local/logs/steamos-select-branch.log"
+
+log() { echo "[$(date --iso-8601=seconds)] $*" | tee -a "$LOGFILE"; }
+
+if [[ $# -eq 1 ]]; then
+  case "$1" in
+    "-c")
+      log "Current branch requested"
+      echo "stable"
+      exit 0
+      ;;
+    "-l")
+      log "Listing available branches"
+      exit 0
+      ;;
+    "rel")
+      log "Legacy branch 'rel' requested"
+      exit 0
+      ;;
+    "stable" | "rc" | "beta" | "bc" | "preview" | "pc" | "main" | "staging")
+      log "Branch '$1' requested"
+      exit 0
+      ;;
+  esac
+fi
+
+echo "Usage: steamos-select-branch <-c|-l|rel|rc|beta|bc|preview|pc|main>" 1>&2
+