fix(ui-models): stop the create card pinning a reference on a blank key

Master's credential-lifecycle work taught the editor card that a pi-ai
profile names `apiKeyEnv` only when a key is actually stored, so a route
left blank keeps its provider-native auth path. The create card kept
writing the derived reference unconditionally, so a route declared for a
credential chain or ADC was born pointing at a reference nothing sets —
and now rendered a red missing-key dot for it.

Both cards apply one rule. The obsolete assertion moves with the behavior
(the with-key case is covered by the neighbouring test), and the merged
Models e2e golden shows the declared route unmarked rather than flagged.

packages/client/ui-models/README.md

@@ -16,7 +16,7 @@ A pi-ai profile's `models` list is edited on the card: one row per model showing
 
 **Fetch available models** asks `llm.discoverModels` about the endpoint the form **currently shows**, including a base URL edited but not yet saved and a key typed but not yet stored, so adding a provider is one pass instead of save-then-return. The reply opens a picker rather than being written: candidates already configured start unchecked, so adopting a selection never overwrites a capacity the user corrected. A provider that cannot be interrogated is a detour, not a dead end — the adapter's own message appears beside the rows, which stay editable by hand.
 
-**Add a custom provider** declares a route pi-ai does not ship. It is its own card rather than the editor with extra fields, because the route id is being chosen here and the settings address does not exist until it is: one `settings.mutate` sets the whole profile at `providers.<route>`, and the key travels separately through `credentials.set` under the same `<ROUTE>_API_KEY` derivation an existing provider uses. What a hand-declared route cannot default gates the create button — a unique **Provider ID**, an endpoint, a protocol, and at least one uniquely-identified model — so the failure names the field while the user is still looking at it. Capacities do not gate it: the adapter's fallbacks size a model the endpoint described by id alone, which is what most listings return. The protocol choices are read out of the namespace's own schema rather than a wire field or a constant, so they cannot drift from the ones the adapter accepts. The card offers the same provider-level reasoning effort the editor card does for this namespace, from one shared control: both write the same profile field, so a route declared without it would have gained the setting only on being reopened.
+**Add a custom provider** declares a route pi-ai does not ship. It is its own card rather than the editor with extra fields, because the route id is being chosen here and the settings address does not exist until it is: one `settings.mutate` sets the whole profile at `providers.<route>`, and the key travels separately through `credentials.set` under the same `<ROUTE>_API_KEY` derivation an existing provider uses. What a hand-declared route cannot default gates the create button — a unique **Provider ID**, an endpoint, a protocol, and at least one uniquely-identified model — so the failure names the field while the user is still looking at it. Capacities do not gate it: the adapter's fallbacks size a model the endpoint described by id alone, which is what most listings return. The protocol choices are read out of the namespace's own schema rather than a wire field or a constant, so they cannot drift from the ones the adapter accepts. The card records the conventional `apiKeyEnv` reference only when a key is typed, the same rule the editor applies, so a route declared for provider-native authentication is not born pointing at a reference nothing will ever set. The card offers the same provider-level reasoning effort the editor card does for this namespace, from one shared control: both write the same profile field, so a route declared without it would have gained the setting only on being reopened.
 
 ## Model Experience