fix: set mongo.in_cluster to true for dev and stg

Both environments use the in-cluster mongo deployed by the helm
chart, so in_cluster should be true. This lets the template
generate the correct FQDN automatically, removing the dependency
on MONGO_URI_DEV and MONGO_URI_STG secrets.

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

Author: Junyi Hou

hack/values-dev.yaml

@@ -6,4 +6,4 @@ cloudflareNodeSelector:
   kubernetes.io/hostname: nuc
 
 mongo:
-  in_cluster: false
+  in_cluster: true

hack/values-stg.yaml

@@ -6,4 +6,4 @@ cloudflareNodeSelector:
   kubernetes.io/hostname: nuc
 
 mongo:
-  in_cluster: false
+  in_cluster: true