LuckPerms compatibility audit: fix event subscription lifecycle, coalesce resyncs

[Blushister]

Summary

Full audit of every LuckPerms touchpoint in the mod (backend selection, runtime checks, event integration, version gating, mod metadata, tests, docs). Two concrete bugs are fixed in this PR; five additional findings are documented in docs/LUCKPERMS_COMPATIBILITY_AUDIT.md without behaviour changes, since they reflect deliberate 1.0.3 policy or low-risk inconsistencies.

Fixed

HIGH - LP event subscription leaked across server lifecycles

LuckPermsService.initServerHooks() subscribed to UserDataRecalculateEvent without keeping the EventSubscription, guarded by a one-way hooksReady flag. After a server stop + start in the same JVM (integrated server opening another world, embedded restart):

• the old subscription stayed registered on the LP event bus with a lambda retaining the dead MinecraftServer (memory leak of the whole server graph);
• hooksReady stayed true, so the new server never re-subscribed - live command-tree resync silently stopped working until JVM restart.

The subscription is now stored, closed on ServerStoppedEvent (closeServerHooks()), and re-created on the next ServerStartedEvent.

MEDIUM - Resync storm on UserDataRecalculateEvent

LP fires this event in bursts for the same user (login, group-inheritance recalculation, messaging sync, web-editor apply). Each event triggered one full ClientboundCommandsPacket re-send plus an INFO log line. Resyncs are now coalesced per player (one packet per burst) and the per-event log is DEBUG.

Documented, intentionally not changed (see audit doc)

• A1 (MEDIUM): permanent degraded flip on the first LP exception (documented invariant) - one transient hiccup disables the LP backend until restart, default fallback deny. A re-probe on /customperm reload is suggested as follow-up.
• A2 (MEDIUM): with LP installed, direct command exposure is disabled, but LuckPerms on NeoForge does not gate vanilla Brigadier commands - aliases become the only way to grant vanilla commands to non-ops. The README workflow about managing normal command perms in LP does not apply to vanilla commands.
• A3 (LOW): version gate rejects qualified versions (5.4.150-SNAPSHOT, 5.5.0-beta) regardless of numeric value - documented as deliberate.
• A4 (LOW): neoforge.mods.toml declares [5.4,) while code enforces 5.4.150+ - LP below 5.4 hard-fails at the loader instead of the graceful fallback.
• A5 (LOW): OP short-circuit asymmetry - internal backend grants any op-2 source; LP backend queries LP verbatim, so /customperm test can show DENIED for an op.

Validation

• ./gradlew compileJava test - build and full pure-Java unit suite pass.
• GameTests are unaffected (LP is compileOnly, the changed code paths only run with LP present); the two fixes require a dev server with the LP jar in run/mods/ per the README manual-validation procedure.