Complete Stage 1: Core Game Loop

- Add GameState enum (LOBBY, ROLE_ASSIGN, IN_GAME, ENDING)
- Add Phase interface with enter/tick/exit/isComplete
- Add GameSession with tick-based phase machine
- Add GameEventBus for internal events
- Add GameManager for session lifecycle
- Add all phases: LobbyPhase, RoleAssignPhase, GameplayPhase, EndgamePhase
- Add role assignment: RoleAssigner, RoleQueue, SpawnPosition
- Add BasePlayer, Survivor, Killer, PlayerState
- Add DBDCommand with /dbd join/leave/create/forcestart/stop
- Update mdbd.java with GameManager and command registration
- Add command definition to paper-plugin.yml
- Mark Stage 1 complete in PLAN.md

src/main/java/dev/loki/phase/EndgamePhase.java

@@ -0,0 +1,31 @@
+package dev.loki.phase;
+
+import dev.loki.core.GameSession;
+
+public class EndgamePhase implements Phase {
+    private int collapseTicks;
+    private boolean complete;
+
+    @Override
+    public void enter(GameSession session) {
+        collapseTicks = session.getConfig().getGame().getInt("endgame.collapse-seconds", 120) * 20;
+        complete = false;
+    }
+
+    @Override
+    public void tick(GameSession session) {
+        collapseTicks--;
+        if (collapseTicks <= 0) {
+            complete = true;
+        }
+    }
+
+    @Override
+    public void exit(GameSession session) {
+    }
+
+    @Override
+    public boolean isComplete() {
+        return complete;
+    }
+}