Add city gameplay, snapshot migrations, administration and Compose operations

.env.example

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+# Optional administrator API; at least 32 random characters. Empty disables it.
+CITYGEN_ADMIN_TOKEN=
+CITYGEN_HOST_IP=127.0.0.1
+CITYGEN_PORT=3000
+CITYGEN_AGENTS=1000
+CITYGEN_MAX_ROOMS=5
+CITYGEN_MEMORY=4g
+CITYGEN_CPUS=4
+CITYGEN_SIM_THREADS=4
+CITYGEN_SAVE_QUOTA_BYTES=2147483648