feat: add multi-world hub system with lobby portals and hub-return addon

Lobby addon detects players in portal zones at X: -15/0/15 and transfers
them to Jamie/Lyla/Mya survival worlds. Hub-return addon gives players a
recovery compass and chat commands (!hub, !lobby) to return to the lobby.

Includes docker-compose.yml for 4 Bedrock servers (lobby + 3 child worlds),
spark pet behavior/resource packs, and updated .gitignore.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -8,5 +8,16 @@ Thumbs.db
 *.swp
 *.swo
 
+# Build artifacts
+*.mcaddon
+*.mcpack
+addon/build/
+
+# Environment
+.env
+
+# Server data (Docker volumes are external, but just in case)
+server-data/
+
 # Claude Code
 .claude/