play_solo.bat: open the mission menu (mech/map/options pickers)

play_solo hardcoded -egg ARENA1.EGG, bypassing the miniconsole front end
that already carries the full pickers: SOLO/RAW-SOLO/HOST-LAN/JOIN-LAN
modes, 8 maps, all 18 mechs, 4 experience levels, colours/badges/patches,
drop zones, advanced damage, time-of-day, weather and mission length.

The bat now launches zero-arg (BT_PLATFORM=glass -> the menu); the menu
relaunches the exe with the generated egg and the cockpit/gauge env
(BT_START_INSIDE/BT_DEV_GAUGES) inherits into the mission child.  Menu-boot
verified with the bat's exact env; the solo menu->mission->menu cycle was
verified at FE landing.  README + the btoperator generated-bat template
updated to match.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/btoperator.py

@@ -852,13 +852,13 @@ class Operator(QMainWindow):
         with open(os.path.join(out_dir, "play_solo.bat"), "w",
                   newline="\r\n") as f:
             f.write(guarded(
-                "rem BT411 -- single-player practice (no network, no "
-                "operator).\n"
-                "rem Edit the -egg below for other maps "
-                "(ARENA2/DBASE/FOGDAY/...).\n",
+                "rem BT411 -- single-player play: opens the MISSION MENU (pick "
+                "mech, map,\n"
+                "rem experience, weather, length; the menu returns after each "
+                "mission).\n",
                 "set BT_START_INSIDE=1\nset BT_DEV_GAUGES=1\n"
                 "set BT_LOG=join.log\n",
-                "..\\build\\Release\\btl4.exe -egg ARENA1.EGG\n",
+                "..\\build\\Release\\btl4.exe\n",
                 "echo.\necho The game has exited.  If it closed unexpectedly,\n"
                 "echo send the operator content\\join.log.\npause\n"))
         self.log.appendPlainText(