Idle imps help: up to five imps at one task, +25% speed per helper (max 200%)

Imps with nothing else to do (no digging, delivering, claiming, repairing or reinforcing of
their own) walk to a task of another imp and help; every 1.5 s they check for own work again.
Claiming floor keeps its priority before helping. Test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/en.lang

@@ -504,3 +504,4 @@ camp.m20.title = The Grand Master
 camp.m20.story = Grand Master Valerian Brightshield waits in his citadel beyond the great river, with the last shard and the gate of the order. He has prayed, polished and prepared for a hundred years. | Destroy his gate, take back the shard and make your core whole again. I will be right behind you. Well behind you.
 camp.epilogue = The last shard sinks into the core, and the darkness breathes again. Somewhere above, the Order of the Lightwatch is writing a very long report. | Crookfinger has made tea. You are whole, master. The underworld is yours.
 lair.arrivals = {0} free beds: new creatures arrive at {1}% speed
+job.help = Helping