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/encoding/utf8/encode_test.ww

@@ -1,6 +1,5 @@
-// encodetest — exercises utf8.encoderune. A failing row aborts via
-// the assert/abort builtin (task #5 @test conversion).
-// Vectors mirror ref/hare/encoding/utf8/encode.ha.
+// Vectors mirror ref/hare/encoding/utf8/encode.ha. A failing row aborts
+// via the assert/abort builtin (task #5 @test conversion).
 
 package utf8_test;