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/utf8.ww

@@ -1,4 +1,4 @@
-// encoding/utf8 — UTF-8 encode/decode. Hare port; see
+// Hare port; see
 // ref/hare/encoding/utf8/{types,rune,encode,decode,decodetable}.ha.
 //
 // The decoder is Hoehrmann's branchless DFA, originally published
@@ -453,4 +453,3 @@ export fn slice(begin: *decoder, end: *decoder) []u8 = {
 export fn position(d: *decoder) i32 = {
 	return d.offs: i32;
 };
-