[nightly-regression] Cover Sparkle no-update delegate paths

[r3dbars]

Summary

• Adds regression coverage for Sparkle updaterDidNotFindUpdate(_:error:) so code 1001 stays on the no-update success path.
• Keeps the existing finish-cycle no-update guard in the same contract test.

Nightly evidence

• Live PostHog last 24h: update_check_finished=41; failure_code=sparkle_1001 accounted for 40 failure_kind=unknown events.
• Current main already contains the code fix; this PR tightens the test guard for the second delegate path.
• Live Sentry unresolved 24h query returned no issues.
• Open product issues still worth watching: Mic audio recording is a lot quiter #500 quiet mic / meeting audio, Long Meetings (approx 2h) don't show #825 long-meeting visibility.

Verification

• git diff --check
• bash build-deps.sh --force
• bash build.sh --no-open
• bash run-tests.sh (3034 passed)
• codex review --uncommitted (no actionable findings; reran full fast tests after rejecting an unsupported filter flag)

[r3dbars]

verdict: no-findings-but-human

Reviewed head 40c69c648e678ab59f1ae0bb0a267e72c5a8b565. Findings: none.

Actions: human signoff because this is a draft PR and touches Sparkle/update observability coverage. No fix pushed.

Checks: reviewed PR metadata, discussion, diff, status checks; repo-hygiene is passing; read repo/test/Observability guidance; ran git diff --check origin/main...origin/codex/nightly-regression-sparkle-no-update-delegates-20260531.

manual_merge_handoff:
head_sha: 40c69c6
verdict: no-findings-but-human
blockers: draft PR and Sparkle/update observability human signoff
checks: gh pr view/diff/checks, repo-hygiene passing, local docs reviewed, git diff --check