core: allow model configurations without npm/api provider details

Makes npm and api fields optional in the provider schema so model definitions

can be more flexible when provider package details aren't needed.

packages/opencode/src/provider/models.ts

@@ -64,7 +64,7 @@ export namespace ModelsDev {
     status: z.enum(["alpha", "beta", "deprecated"]).optional(),
     options: z.record(z.string(), z.any()),
     headers: z.record(z.string(), z.string()).optional(),
-    provider: z.object({ npm: z.string(), api: z.string() }).optional(),
+    provider: z.object({ npm: z.string().optional(), api: z.string().optional() }).optional(),
     variants: z.record(z.string(), z.record(z.string(), z.any())).optional(),
   })
   export type Model = z.infer<typeof Model>