AtlasSpigot 26.2 - v7 (join throughput + panel JVM flags)

Change from v6:

• max-joins-per-tick raised 5 -> 25: at the default, a mass-reconnect event queues behind an artificial ~100/sec join ceiling. Doesn't change any gameplay mechanic, just how fast the connection queue drains under a big simultaneous-join spike.
• Added PANEL_STARTUP_FLAGS.md: the user's actual Spaceify log showed the panel generates its own java command (-Xms128M -XX:MaxRAMPercentage=95.0 ...), which completely bypasses start.sh's G1GC tuning. This file has the same tuning adapted to a panel's dynamic RAM-percentage sizing style.

Same jar as v6 (no source changes this round).