fix(inventory): keep user-defined custom providers in model dedup

The #45954 model-dedup builds `user_models` from every is_user_defined
row, then strips those model IDs from every row where is_aggregator(slug)
is True. But is_aggregator() returns True for *every* `custom:*` slug, and
list_authenticated_providers emits named custom providers with slug
`custom:<name>` and is_user_defined=True. So a user's own custom provider
is treated as an aggregator and filtered against user_models — which holds
exactly its own models (the row helped build that set). Every model is
removed, the row drops to zero, and the provider disappears from the model
picker.

Guard the dedup loop to skip is_user_defined rows: a user's configured
provider is never an aggregator duplicate of itself. Built-in aggregators
(openrouter, etc.) are still deduped as before. Adds a regression test.

hermes_cli/inventory.py

@@ -178,6 +178,14 @@ def build_models_payload(
                 user_models.update(m.lower() for m in (row.get("models") or []))
         if user_models:
             for row in rows:
+                # A user's own configured provider is never an "aggregator
+                # duplicate" of itself: user_models is built from these very
+                # rows, and is_aggregator() reports True for every custom:*
+                # slug.  Without this guard the dedup strips a user-defined
+                # custom provider's entire model list (all of it lives in
+                # user_models), emptying its picker row.
+                if row.get("is_user_defined"):
+                    continue
                 slug = row.get("slug", "")
                 if not _is_aggregator(slug):
                     continue