chore(desktop): remove dead provider prop and delegate default label to shared formatter

StandaloneAgentCard's resolveAgentCardModelLabel call had a top-level
provider field that the helper never reads — when input.agent is present,
it reads provider from input.agent.provider instead. Remove the dead field
and its three redundant copies in linked-agent regression tests.

Replace the inline template at AgentConfigFields:804 with a call to
formatDefaultModelLabel, which is already regression-tested for the
provider-scoped Databricks-name leak. Drop the now-unused resolveModelLabel
import. Derive fallbackModelLabel as a const to keep the JSX clean and
within the file-size ratchet.

Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

desktop/src/features/agents/lib/agentCardModelLabel.test.mjs

@@ -119,7 +119,6 @@ test("resolveAgentCardModelLabel — openai agent inheriting a Databricks-named
   const label = resolveAgentCardModelLabel({
     agent: { modelSource: "global", model: null, provider: "openai" },
     personaModel: null,
-    provider: "openai",
     defaultModel: "databricks-gpt-5-5",
   });
   assert.equal(label, "Default model (databricks-gpt-5-5)");
@@ -129,7 +128,6 @@ test("resolveAgentCardModelLabel — anthropic agent inheriting a Databricks-nam
   const label = resolveAgentCardModelLabel({
     agent: { modelSource: "global", model: null, provider: "anthropic" },
     personaModel: null,
-    provider: "anthropic",
     defaultModel: "databricks-gpt-5-5",
   });
   assert.equal(label, "Default model (databricks-gpt-5-5)");
@@ -139,7 +137,6 @@ test("resolveAgentCardModelLabel — databricks_v2 agent inheriting a Databricks
   const label = resolveAgentCardModelLabel({
     agent: { modelSource: "global", model: null, provider: "databricks_v2" },
     personaModel: null,
-    provider: "databricks_v2",
     defaultModel: "databricks-gpt-5-5",
   });
   assert.equal(label, "Default model (GPT-5.5)");

desktop/src/features/agents/ui/AgentConfigFields.tsx

@@ -48,7 +48,7 @@ import {
 } from "@/features/agents/ui/agentConfigControls";
 import { PersonaProviderApiKeyField } from "@/features/agents/ui/PersonaProviderApiKeyField";
 import { usePersonaModelDiscovery } from "@/features/agents/ui/usePersonaModelDiscovery";
-import { resolveModelLabel } from "@/features/agents/lib/formatAgentModelLabel";
+import { formatDefaultModelLabel } from "@/features/agents/lib/agentCardModelLabel";
 import {
   BUZZ_AGENT_THINKING_EFFORT,
   getProviderEffortConfig,
@@ -284,6 +284,9 @@ export function AgentConfigFields({
     () => getGlobalModelFallback(bakedEnv, effectiveProvider, config.env_vars),
     [bakedEnv, config.env_vars, effectiveProvider],
   );
+  const fallbackModelLabel = fallbackModel
+    ? formatDefaultModelLabel(fallbackModel, effectiveProvider || undefined)
+    : undefined;
   const modelField = fieldModel.fields.find(
     (field) => field.kind === "model" && field.render === "control",
   );
@@ -799,11 +802,7 @@ export function AgentConfigFields({
         <div className={showDescriptions ? fieldClassName : undefined}>
           <AgentModelField
             allowDefaultModel={fallbackModel !== null}
-            defaultModelLabel={
-              fallbackModel
-                ? `Default model (${resolveModelLabel(fallbackModel, undefined, effectiveProvider || undefined)})`
-                : undefined
-            }
+            defaultModelLabel={fallbackModelLabel}
             disableSelectDuringDiscovery={disableModelSelectDuringDiscovery}
             disabled={dependentFieldsDisabled}
             discoveredModelOptions={

desktop/src/features/agents/ui/UnifiedAgentsSection.tsx

@@ -393,7 +393,6 @@ function StandaloneAgentCard({
       modelLabel={resolveAgentCardModelLabel({
         agent,
         personaModel: null,
-        provider: agent.provider,
         defaultModel,
       })}
       onClick={() => {