Link console capture race fix to issue #4808

[Widthdom]

Summary

• Associate the shared-gate console restoration fix already present on the latest main with Full-suite ConsoleCapture timeout test can restore a different writer under load #4808.
• Rename the regression test so its discovery identity retains both Full-suite Console.Error capture can leave a disposed global writer #4749 and Full-suite ConsoleCapture timeout test can restore a different writer under load #4808 provenance.
• Consolidate the existing bilingual changelog fragment for Full-suite ConsoleCapture test can race with parallel console mutation #4800 and Full-suite ConsoleCapture timeout test can restore a different writer under load #4808.

Root cause

The timeout test originally captured and asserted the process-global console writers outside the shared ownership gate. Under full-suite parallel load, another capture could temporarily replace a writer, making the expected writer identity stale. The latest main now snapshots and asserts the writers under TestConsoleLock.Gate; this PR records that the same stabilization resolves #4808 after the implementation landed concurrently through #4800.

Validation

• Full Release solution run after the functional fix: net8.0 — 10,376 passed, 7 skipped, 0 failed; net9.0 — 9,918 passed, 404 skipped, 0 failed.
• ConsoleCaptureTests on the final latest-main branch: 8/8 passed on both net8.0 and net9.0.
• Renamed regression test during Codex review: 1/1 passed on both net8.0 and net9.0.
• dotnet run --project tools/CodeIndex.Changelog -- check: 49 fragments validated.
• git diff --check origin/main..HEAD: passed.
• Codex adversarial review: No blocking/actionable issues found.

Documentation and changelog

• Extends the existing bilingual fragment as changelog.d/unreleased/4800-4808.fixed.md.
• The latest main already contains synchronized English/Japanese TESTING_GUIDE.md guidance for snapshotting and asserting global console writers under the shared gate.
• CHANGELOG.md is unchanged.

Follow-up candidates

• None.

Fixes #4808