feat(FN-3006): merge fusion/fn-3006

Commits merged:
- fix(FN-3006): complete Step 3 — repair dashboard typecheck mapper signatures
- test(FN-3006): complete Step 2 — cover Use default reselection flow
- feat(FN-3006): complete Step 1 — resolve default model selection target

Files changed:
.../app/components/ModelOnboardingModal.tsx        | 24 ++++++---
 packages/dashboard/app/components/QuickChatFAB.tsx | 13 +++--
 .../dashboard/app/components/SettingsModal.tsx     | 24 ++++++---
 .../app/components/__tests__/QuickChatFAB.test.tsx | 61 ++++++++++++++++++++++
 4 files changed, 103 insertions(+), 19 deletions(-)

Fusion-Task-Id: FN-3006

packages/dashboard/app/components/ModelOnboardingModal.tsx

@@ -25,14 +25,22 @@ import { LoginInstructions } from "./LoginInstructions";
 import { CustomProviderForm } from "./CustomProviderForm";
 import { appendTokenQuery } from "../auth";
 
-const mapLegacyCustomProviderToConfig = (provider: CustomProvider): CustomProviderConfig => ({
-  id: provider.id,
-  name: provider.name,
-  baseUrl: provider.baseUrl,
-  api: provider.apiType === "anthropic-compatible" ? "anthropic-messages" : "openai-responses",
-  apiKey: provider.apiKey,
-  models: provider.models?.map((model) => ({ id: model.id, name: model.name })) ?? [],
-});
+const mapLegacyCustomProviderToConfig = (
+  provider: CustomProvider | CustomProviderConfig,
+): CustomProviderConfig => {
+  if ("api" in provider) {
+    return provider;
+  }
+
+  return {
+    id: provider.id,
+    name: provider.name,
+    baseUrl: provider.baseUrl,
+    api: provider.apiType === "anthropic-compatible" ? "anthropic-messages" : "openai-responses",
+    apiKey: provider.apiKey,
+    models: provider.models?.map((model) => ({ id: model.id, name: model.name })) ?? [],
+  };
+};
 
 /** Provider-specific API key setup metadata for onboarding form rendering */
 interface ApiKeyInfo {