fix: add CAMELEER_JWT_SECRET for cameleer3-server

The server needs this to derive its Ed25519 signing key. Without it,
startup fails with 'Empty key'.

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

docker-compose.yml

@@ -99,6 +99,7 @@ services:
       SPRING_DATASOURCE_PASSWORD: ${POSTGRES_PASSWORD:-cameleer_dev}
       CLICKHOUSE_URL: jdbc:clickhouse://clickhouse:8123/cameleer
       CAMELEER_AUTH_TOKEN: ${CAMELEER_AUTH_TOKEN:-default-bootstrap-token}
+      CAMELEER_JWT_SECRET: ${CAMELEER_JWT_SECRET:-cameleer-dev-jwt-secret-change-in-production}
       CAMELEER_TENANT_ID: ${CAMELEER_TENANT_SLUG:-default}
     labels:
       - traefik.enable=true