add dev resources; plumb GUI_ENV_FILE/API_ENV_FILE/API_DESI_DATA into run targets

resources/dev/api.env.example

@@ -0,0 +1,8 @@
+# Example API environment — passed via API_ENV_FILE (see root Makefile).
+#
+# The API also reads API_DESI_DATA from the environment (set by the root
+# Makefile to resources/dev/desi_subset.json by default), so it is not
+# repeated here. Values here win unless the same key is already set in the
+# real process environment.
+
+API_BIND_ADDR=127.0.0.1:8080