Add player presence reconciliation for proxy servers

[frederickbaier]

Why

The controller already implements player presence reconciliation — it periodically sends compare requests to each proxy to detect drift between its known player state and reality. This handles two failure modes: lost disconnect events (stale ghost players in the controller) and lost login events (connected players invisible to the network). Until now, the proxy-side counterpart to answer these requests did not exist.

What this PR does

Proxy-side presence responder

Implements the proxy-side handler for the controller's presence reconciliation protocol:

1. The controller sends a PresenceCompareRequest containing an FNV-32a hash of the players it believes are on a given proxy
2. The proxy computes the same hash over its actual connected players
3. If the hashes match, the proxy responds with match: true — no further action needed
4. If they differ, the proxy responds with the full player snapshot list, allowing the controller to reconcile: re-triggering logins for unknown players and cleaning up stale entries

The hash-first approach minimizes NATS traffic during normal operation — the full player list is only transferred when there's actually a discrepancy.

New components:

• ProxyPresenceResponder — subscribes to {networkId}.server.{serverId}.presence.compare and handles compare requests. Owned by the proxy plugins (Velocity / BungeeCord) directly, since only proxies need to respond — this avoids every CloudApi.create() caller (lobby plugins, minigame plugins, etc.) creating redundant NATS subscriptions.
• ProxyPresenceTracker — tracks stable per-player metadata (login timestamp, session ID) that isn't available from the platform API at snapshot time
• ProxyPresencePlayer / ProxyPresencePlayerProvider — immutable player snapshot and provider interface

Other improvements

• CloudApi extends AutoCloseable — CloudApiImpl.close() properly shuts down cache, event listeners, and the NATS connection, guarded by AtomicBoolean to prevent double-close
• PlayerIntegration accepts CloudApiImpl directly — removes the runtime type check and cast, since only proxy plugins use it
• SimpleCloudRuntime utility — centralizes environment variable access (SIMPLECLOUD_UNIQUE_ID, SIMPLECLOUD_GROUP, SIMPLECLOUD_NUMERICAL_ID) replacing scattered System.getenv() calls
• BungeeCord login fix — was incorrectly passing connection.getListener().getDefaultServer() where the locale parameter was expected