make production/devel mode gated by env var

.envrc

@@ -1,2 +1,3 @@
 export DATABASE_URL="sqlite:lib/crossfire.sqlite"
+export CROSSFIRE_DEVEL=1
 [ -d lib ] || mkdir -p lib/projects

crossfire/server.rkt

@@ -32,7 +32,7 @@
 
 (define *server-node-id* 0)
 
-(define *production?* #f)
+(define *production?* (not (getenv "CROSSFIRE_DEVEL")))
 
 ;; XXX : platform-specific
 (define *config-root* (if *production?* "/etc/" "etc/"))