feat(bench): add datapack-driven harness v2 with boot checks

xdotool chat injection silently fails under KDE Wayland/Xwayland, so the
v1 harness recorded runs whose scene commands never executed. v2 drives
scenes from a generated world datapack, detects crashes, aligns MangoHud
CSVs by file birth time, flags vsync/backup/low-n windows, and records
full run metadata to JSONL; analyze.py applies the BENCH-MATRIX win rule.

analysis/client-perf/harness/tests/fixtures/crash.log

@@ -0,0 +1,4 @@
+[14Oct2026 22:21:53.972] [modloading-worker-0/ERROR] [net.neoforged.fml.javafmlmod.FMLModContainer/LOADING]: Failed to create mod instance. ModID: midnightlib, class eu.midnightdust.core.MidnightLib
+[14Oct2026 22:21:57.100] [Render thread/FATAL] [net.minecraft.client.Minecraft/]: Unreported exception thrown!
+[14Oct2026 22:21:57.200] [Render thread/ERROR] [net.neoforged.fml.ModLoader/]: Cowardly refusing to send event net.neoforged.neoforge.client.event.RenderFrameEvent to a broken mod state
+[14Oct2026 22:21:57.300] [Render thread/INFO] [mixin/]: harmless line mentioning FATAL in text only