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/errors/errno_test.ww

@@ -1,6 +1,3 @@
-// errnotest — exercises [[errors.errno]] and the [[errors.opaque_]]
-// tail. Run with `out/bin/ww run lib/errors/errnotest.ww`.
-//
 // Parallel `[N]T` arrays of (errno, expected-tag) rather than a
 // `[N]struct{...}` table — the cstage cgen's chained `arr[i].field`
 // store gap (task #6). [[errtag]] collapses each named-void variant to
@@ -42,7 +39,6 @@ fn errtag(e: errors.error) int = {
 	};
 };
 
-// ---- errno → named condition --------------------------------------
 @test fn mapping() void = {
 	let ins: [12]os.errno;
 	ins[0]  = os.ECONNREFUSED;
@@ -85,7 +81,6 @@ fn errtag(e: errors.error) int = {
 	};
 };
 
-// ---- unmapped errno → opaque_ tail --------------------------------
 @test fn opaquetail() void = {
 	// EIO (5) is outside the mapped set, so it wraps opaque_.
 	let e: errors.error = errors.errno(5);
@@ -98,7 +93,6 @@ fn errtag(e: errors.error) int = {
 	};
 };
 
-// ---- os.strerror mapped path --------------------------------------
 @test fn strerrortext() void = {
 	assert(!(!streq(os.strerror(os.ENOENT), "No such file or directory")));
 	assert(!(!streq(os.strerror(os.EINVAL), "Invalid argument")));