fix(kong): SERVICE_NAMESPACE=default in conf/dev overlay caused kong to deploy to default ns

conf/dev/knoe.cfg had a stale SERVICE_NAMESPACE=default written by a prior TUI session.
Also guard _service_namespace() so the value 'default' is never returned — it is never
a valid service namespace and signals a stale generated config.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

conf/dev/knoe.cfg

@@ -5,5 +5,5 @@
 CLUSTER_ENV = dev
 NAMESPACE = knoe-db
 DATABASE_NAMESPACE = knoe-db
-SERVICE_NAMESPACE = default
+SERVICE_NAMESPACE = knoe-system
 CLUSTER_NAME = knoe-db

knoe/core/actions.py

@@ -308,8 +308,12 @@ class KnoeInstaller:
         )
         if ns.startswith("${") and ns.endswith("}"):
             ns = ""
+        if ns == "default":
+            ns = ""
         if not ns:
             ns = (os.environ.get("SERVICE_NAMESPACE") or "").strip()
+        if ns == "default":
+            ns = ""
 
         if ns:
             return ns