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/memio/memio.ww

@@ -122,8 +122,6 @@ export fn dynamicfrom(buf: []u8) stream = {
 	return r;
 };
 
-// ---- vtable callbacks ----------------------------------------------------
-
 // readfn — recover the stream from the io.stream's `*vtable` via the
 // intrusive offset-0 cast. Single fn over the common header (Hare's
 // single `read` at ref/hare/memio/stream.ha:103); fixed and dynamic
@@ -247,11 +245,6 @@ fn dynamicgrow(d: *stream, need: i32) void = {
 	d.cap = newcap;
 };
 
-// ---- accessors over the common `stream` header -----------------------
-//
-// Single fn each: Hare's string/reset/buffer/borrowedread all take
-// `*stream` and read the flat header.
-
 // string — bytes written so far, as a str view (buf[0..pos]).
 //
 // Mirrors ref/hare/memio/stream.ha:81 string(in: *stream). Hare returns