ScriptableBoss

Adapts an EliteEntity boss for the shared Magmacore scripting runtime (ScriptInstance). This replaces the old self-contained LuaPowerInstance: the lifecycle (Lua VM, hook dispatch, the lazy context metatable, the 50ms watchdog, owned tasks, shutdown) is now Magmacore's, while the rich boss-specific context tables are still produced by the original builder classes (LuaPowerEntityTables, LuaPowerContextTables, LuaPowerScriptApi, LuaPowerSupport) — reused verbatim — so the full boss scripting API is preserved.