docs: library comments say what the scanner and resolver do, not how they came to be (#6277)

Rewrites the internal/library comment blocks to rule 32. Task, milestone,
decision and rule ids are gone; the incidents behind them are restated as
the constraint they left (why a file is deleted before its row, why the
missing mark is a mark, why duplicates block on duration). Counts and
album names from one library are dropped from production comments; test
comments keep the names their fixtures use. The tagReadVersion log keeps
each version's before and after, without the measurements.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/duplicate_merge_test.go

@@ -83,7 +83,8 @@ func newMergeFixture(t *testing.T) mergeFixture {
 	}
 	f.alice, f.bob = user("merge-alice"), user("merge-bob")
 
-	// Alice liked both copies, the removed one first; Bob liked only the removed one.
+	// Alice liked both copies, the removed one first; Bob liked only the
+	// removed one.
 	f.aliceEarlierLikeOnRem = time.Now().Add(-72 * time.Hour).UTC().Truncate(time.Microsecond)
 	mustExec(`INSERT INTO general_likes (user_id, track_id, liked_at) VALUES ($1, $2, $3), ($1, $4, now()), ($5, $2, now())`,
 		f.alice.ID, f.remove.ID, f.aliceEarlierLikeOnRem, f.keep.ID, f.bob.ID)
@@ -144,9 +145,8 @@ func (f mergeFixture) count(t *testing.T, sql string, args ...any) int {
 	return n
 }
 
-// The #3911 proof: after a merge, every piece of history the removed copy held
-// is on the copy kept, nothing is doubled, and the removed copy — row and file —
-// is gone.
+// After a merge, every piece of history the removed copy held is on the copy
+// kept, nothing is doubled, and the removed copy — row and file — is gone.
 func TestMergeDuplicateGroup_Integration(t *testing.T) {
 	f := newMergeFixture(t)
 	ctx := context.Background()
@@ -208,8 +208,8 @@ func TestMergeDuplicateGroup_Integration(t *testing.T) {
 		t.Errorf("the kept copy's own house weight was overwritten")
 	}
 
-	// Similarity: rewritten onto the kept copy, no duplicate edge, no self-edge,
-	// nothing left pointing at the removed copy.
+	// Similarity: rewritten onto the kept copy, no duplicate edge, no
+	// self-edge, nothing left pointing at the removed copy.
 	if n := f.count(t, `SELECT count(*) FROM track_similarity WHERE track_a_id = $1 AND track_b_id = $2 AND source = 'listenbrainz'`,
 		f.keep.ID, f.other.ID); n != 1 {
 		t.Errorf("listenbrainz edge keep→other = %d rows, want exactly 1", n)