Post-match lobby cleanup and network concede fixes

[MostCromulent]

Summary

Addresses Phase 0.5 of the network draft/sealed implementation plan — hardening existing network match lifecycle before adding new game modes. Also fixes several pre-existing network concede bugs observed during testing. See discussion at Card-Forge/forge#9861 (comment) and follow-up.

Issues addressed

• No lobby cleanup after network match — the previous match's state lingered in the lobby after returning. Added onMatchOver callback to reset lobby state (null hostedMatch, un-ready slots, clear player GUIs, push lobby update to clients).

• Client concede dialog never appeared — instanceof PlayerControllerHuman excluded NetGameController, so the concede confirmation was silently skipped. Broadened the check to include network controllers.

• Client concede force-quit both players — client sent a premature nextGameDecision(QUIT) before the server processed the concede, ending the match for both. Network games now let the server drive the game-end flow.

• Game thread blocked after concede — only the conceding player's input latch was released, but the game thread could be waiting on the other player's input queue. Now releases all players' input latches.

• Remote client never saw win/lose screen — game-end events were buffered in GameEventForwarder and never flushed. Added explicit flush after the game loop exits.

• NPEs from late-arriving messages — protocol messages arriving after cleanup caused NullPointerException on the server. Added null guards in the protocol handler with null reply for non-void methods.

Why these changes are safe

• Lobby cleanup only runs when a match ends via NextGameDecision.QUIT — the same path that already calls endCurrentGame(). It adds cleanup after existing teardown, doesn't change teardown order.
• Concede dialog fix only affects network clients. Local games still go through the PlayerControllerHuman path with the per-player outcome check. No behavior change for single-player or local multiplayer.
• Skipping premature QUIT only applies to network games (isNetGame() guard). Local games still send nextGameDecision synchronously as before.
• Input latch release is idempotent — CountDownLatch.countDown() on an already-released latch is a no-op.
• Protocol null guards only fire after cleanup when controllers are already gone. During normal gameplay, getToInvoke() and getClient() always return non-null.

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