test(app): restore ThreadRow resolver spy

[ymichael]

Human comments

What was wrong

The archived-thread title regression added in #2527 replaced the shared sdk.threads.resolveMentions method without restoring it. Because later tests in ThreadRow.test.tsx reuse that SDK object, they could inherit the canned result and become order-dependent or falsely green.

What changed

The resolver regression now restores its exact spy in finally, including when rendering or an assertion throws. The file teardown also asserts that the shared resolver is no longer mocked, preserving the isolation invariant for future tests. This is test-only: no production, wire, CLI, SDK, or documentation behavior changed.

How you verified

• Before the cleanup, the targeted Turbo run failed its teardown isolation assertion, and the full file reported 42 failures after the leaking test.
• pnpm exec turbo run test --filter=@bb/app -- src/components/sidebar/ThreadRow.test.tsx — 71 passed.
• pnpm exec prettier --check apps/app/src/components/sidebar/ThreadRow.test.tsx — passed.
• git diff --check origin/main...HEAD — passed.
• Rebasing from ad79bbb5 onto current origin/main preserved the stable patch ID exactly.

Follow-up to #2527; no issue.

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