chore(tests): remove no-op example tests + audit notes

[Aryansharma28]

Summary

Removes two example tests that produce no signal but consume CI time on every PR:

• `javascript/examples/vitest/tests/vegetarian-recipe-realtime.test.ts` — entire file is a single `it.skip`. Nothing runs.
• `multilingual-agent.test.ts` > `handles adversarial users and conversational chaos` — wrapped in `try { expect(...).toBe(true) } catch { expect(true).toBe(true) }` with a `// TODO: this test is flaky, let it pass for now` comment. Always passes; up to 360s timeout per run; ~12 turns of live LLM calls.

Follow-up to #423 (which removed the flaky `multiturn-10-scripted.test.ts`).

Audit notes — flagged for discussion (not in this PR)

These came up in the audit but I'm not removing them unilaterally:

• `prefill-error-repro.test.ts` — bug-repro test sitting in examples. Skipped without `ANTHROPIC_API_KEY`. Probably belongs in a regression suite inside the SDK, not in user-facing examples.
• Several live-LLM example tests (`travel-agent`, `vegetarian-recipe-agent`, `false-assumptions`, `multilingual-agent` happy-path test) run on every PR via `Test (Examples)` job. They're useful as docs but introduce flake risk on unrelated PRs (e.g. dependency-pin PRs). Worth considering moving the example job to a nightly/manual workflow.
• ~30 `it.todo(...)` placeholders across the multimodal test files — harmless, but most have been there indefinitely with no implementation. Could prune for tidiness.

Test plan

• CI green.
• No reduction in meaningful coverage (both removed tests were pure no-ops).

[github-actions]

Automated low-risk assessment

This PR was evaluated against the repository's Low-Risk Pull Requests procedure.

• Scope: Deletes javascript/examples/vitest/tests/vegetarian-recipe-realtime.test.ts and removes the 'handles adversarial users and conversational chaos' test block from javascript/examples/vitest/tests/multilingual-agent.test.ts (test/examples-only changes).
• Exclusions confirmed: no changes to auth, security settings, database schema, business-critical logic, or external integrations.
• Classification: low-risk-change under the documented policy.

The PR only removes example test code: a fully skipped realtime example and an always-passing/flaky adversarial scenario that consumed CI time. It does not modify auth/authorization, secrets, DB schemas, business logic, or external integrations and is limited to test/examples cleanup, so it meets the low-risk criteria.

This classification allows merging without manual review once all required CI checks are passing and branch protection rules are satisfied.