fix(signals): include queue-growth risk in medium burden tier

[philluiz2323]

Closes #465.

buildBurdenForecast's level ternary OR's queueGrowthRisk into the critical (>=80) and high (>=55) tiers but the medium tier checked only projectedReviewLoad >= 25. So a small unreviewable/collision-heavy queue with moderate growth risk (queueGrowthRisk in [25, 55)) but low review load was classified low instead of medium — the single tier that broke the OR pattern.

Example: 5 open PRs, no linked issues, updated 10 days ago (not recent, not stale) -> projectedReviewLoad = 15, queueGrowthRisk = 25 -> previously low, now medium.

Change

• Add || queueGrowthRisk >= 25 to the medium tier, matching the critical/high tiers.
• Add a regression test asserting the QGR-driven medium case (fails on the old code, which returned low).

Verification

• Full unit suite green (1255 passed). Existing low/critical forecast assertions unchanged.

[ghost]

Note

Gittensory Gate skipped

PR closed before full evaluation. No late first comment was created.

Signal	Result	Evidence	Action
Gate result	⚠️ Skipped	#466 is no longer open.	No action.

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Checked by Gittensory, a quiet PR intelligence layer for OSS maintainers.

[JSONbored]

@philluiz2323 this is ready.

A few notes:

• The medium tier now treats moderate queue-growth risk consistently with the high and critical tiers.
• The added test covers the exact under-classification case from #465.
• No code changes requested.