lib: banner purge + WHY-only comment sweep (rule 8)

Every // ---- section banner dies (132 -> 0): names carry the WHAT.
Narration deleted (filename restatements, run-with lines, what-the-
next-line-does); every ref/hare cite, task cite, divergence, ABI/
layout contract, and ownership qualifier kept (borrowed-view lines
restored where the sweep over-cut). Comment-only proven: all 442
walk-workdir .s and 32 import-probe .s byte-identical before/after;
libbyteid 56-roster all-ID.

lib/strings/concat_test.ww

@@ -58,7 +58,6 @@ import os;
 	};
 };
 
-// ---- join -------------------------------------------------------------
 // ref/hare/strings/concat.ha:64. Rows mirror Hare's @test fn join
 // (0-arg, 1-arg, empty-sep, 3-arg.) plus 2-arg, all-empties, long sep,
 // multibyte, empty-mid (delim still inserted around the empty slot).
@@ -111,4 +110,3 @@ import os;
 		i += 1;
 	};
 };
-