fix(tests): repair test regressions from zod v3 downgrade

- Fix zod/v4 imports in background-task schema tests
- Remove ZWSP prefix from agent-key-remapper test (fixed in #3136)
- Use toMatchObject for openai-only catalog tests (fallback_models added by #3144)
- Replace z.toJSONSchema (zod v4) with zodToJsonSchema (zod v3 compat)
- Fix task-list.ts type narrowing for zod v3 inferred types

src/config/schema/background-task-circuit-breaker.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { ZodError } from "zod/v4"
+import { ZodError } from "zod"
 import { BackgroundTaskConfigSchema } from "./background-task"
 
 describe("BackgroundTaskConfigSchema.circuitBreaker", () => {

src/config/schema/background-task.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { ZodError } from "zod/v4"
+import { ZodError } from "zod"
 import { BackgroundTaskConfigSchema } from "./background-task"
 
 describe("BackgroundTaskConfigSchema", () => {