fix: search ~/.steam/root and Flatpak data/Steam roots

Layouts from PR #1 (Manjaro report), folded into tools/steam_paths.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014TkQMhvEyoFqKzeCC69N6o

tools/steam_paths.py

@@ -27,8 +27,10 @@ PROTON_PROFILE = "compatdata/" + APP_ID + "/pfx/drive_c/users/steamuser/Saved Ga
 STEAM_ROOTS_UNDER_HOME = [
     ".local/share/Steam",
     ".steam/steam",
+    ".steam/root",
     ".steam/debian-installation",
     ".var/app/com.valvesoftware.Steam/.local/share/Steam",
+    ".var/app/com.valvesoftware.Steam/data/Steam",
     ".snap/steam/common/.local/share/Steam",
     "snap/steam/common/.local/share/Steam",
 ]