fix: Provider.models is a Record keyed by modelID, not an array

Per the OpenCode server docs (GET /config/providers), each Provider's
'models' is { [modelID: string]: Model } (a Record), so model IDs can be
referenced as strings (matching the 'default' map of providerID ->
modelID). Our code treated it as Model[], which:
  1. crashed with 'p.models is not iterable' on real responses, and
  2. after the previous Array.isArray guard, skipped EVERY provider
     (a Record is never an array), so the inline picker showed nothing.

Update types.ts (OpenCodeProvider.models -> Record, add OpenCodeModel,
add optional 'default' map to the response) and rewrite
flattenProviders to iterate Object.keys(p.models). Update test fixture
to the Record shape.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/types.ts

@@ -47,12 +47,27 @@ export interface OpenCodeFailure {
 
 export type OpenCodeResponse = OpenCodeSuccess | OpenCodeFailure;
 
-/** Response from GET /opencode-bridge/providers. */
+/** Response from GET /opencode-bridge/providers (proxies OpenCode /config/providers).
+ *
+ * Per the OpenCode server docs, `/config/providers` returns
+ * `{ providers: Provider[], default: { [providerID]: modelID } }`. Each
+ * `Provider.models` is a Record keyed by modelID (NOT an array), so we
+ * can reference a model by its string ID (also matching `default[providerID]`).
+ */
+export interface OpenCodeModel {
+  id: string;
+  name?: string;
+  [k: string]: unknown;
+}
+
 export interface OpenCodeProvider {
   id: string;
-  models: { id: string; [k: string]: unknown }[];
+  name?: string;
+  source?: string;
+  models: { [modelID: string]: OpenCodeModel };
 }
 
 export interface OpenCodeProvidersResponse {
   providers: OpenCodeProvider[];
+  default?: { [providerID: string]: string };
 }