The queue:check sentence names the check slots in force, not "one lane" #4850

Intent: the queue:check sentence says how many check slots the forge has, so whoever reads it does not chase a lane that is not stuck.

Found while diagnosing #4784: laneSentence in src/kernel/vitals.ts always says "N checks wait behind one lane; … the lane runs #X", but production runs about 7 checks at once (checks.concurrency). The sentence names only the first running check, so a full lane of seven looked like one slow lane.

Done:

• [ ] the sentence names the slot count in force (capacityValue(db, "checks.concurrency")) and how many run now — e.g. "11 checks wait for 7 slots, all busy; the oldest since 01:04; the longest running is #4656 at 5 min (limit 60)" — and says "one lane" only when there is one slot
• [ ] the queue:check cause key is unchanged, so the sentinel does not open a new issue for it
• [ ] test/ covers one slot and several slots

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.