Preserve queued chat translations during bursts

[sappho192]

What changed

• Removed the policy that cancelled the in-flight chat translation whenever another message was waiting.
• Kept the existing single-consumer semaphore and bounded FIFO queue so messages are translated in arrival order.
• Retained MiLMMT's independent 30-second inference timeout and existing queue capacity limits.

Why

A decrypted live log from a short chat burst showed that all 184 messages entered and left the queue, but 13 dequeued messages were discarded by the superseded-translation cancellation path. Four of those translations had already completed before their results were discarded. The maximum queue depth was only 23, with no capacity drops or translation errors.

Impact

During chat bursts, translations may appear later as the FIFO backlog drains, but pending messages no longer cancel and discard earlier translations.

Validation

• dotnet restore src\IronworksTranslator\IronworksTranslator.sln
• dotnet build src\IronworksTranslator\IronworksTranslator.sln -c Debug --no-restore — 0 warnings, 0 errors
• dotnet test tests\IronworksTranslator.Tests\IronworksTranslator.Tests.csproj -c Debug --no-build --no-restore — 174/174 passed
• git diff --check

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.