Stop the listings and their chapters stating fixed defects as fact

You were right that this was still everywhere. The two `.bas` files carried
their workarounds as present-tense statements about the interpreter -- "a name
first created inside a GOSUB costs a value slot that is never handed back",
"writing PAST the terminator of a short row draws nothing at all", "SSHAPE and
GSHAPE ignore the subscript on a string array", "a FOR inside a BEGIN block does
not survive the RETURN" -- and every one of those is now false. A comment that
lies is worse than no comment, and these were the first thing anybody opening
the files would read.

**The characters game takes the geometry fix.** `CW# = 16` becomes `CW# =
RGR(3)`, and the grid comes from `RWINDOW`, so the game fits whatever window and
font the host gives it. That was the one thing in the listing that would break on
a different font, and `RGR(3)` and `RWINDOW` were added to the interpreter
because of it -- leaving the constant in place while Chapter 17 teaches the
function was the inconsistency worth closing. `RGR(1)` still comes first so a
build with no graphics device refuses by naming the device that is missing.

Everything else in both listings keeps its shape and says why. Declaring every
name up front, guarding loops with `GOTO`, six scalars for six brick stamps: none
is forced any more and none costs anything, so they stay, with the comments
marking which rules stand and which are history. The sprites header's five traps
are marked FIXED where they are fixed.

The chapters follow: Chapter 17 Step 2 no longer says "the listing still has
`CW# = 16`", and Chapter 18's trap section is "five things that did not do what
they looked like" with the two that still stand named up front rather than left
to be counted.

Verified: Chapter 17 Step 2's block is once again verbatim from the listing, so
every quoted fragment in both chapters matches its source with no exceptions;
both games run 40 seconds on the SDL frontend with no error line; both suites
green in both configurations; `docs_examples` and `docs_screenshots --check`
pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/18-tutorial-breakout-artwork.md

@@ -623,14 +623,15 @@ RETURN
 
 A silenced voice costs nothing to issue. One line beats eleven scattered through the game.
 
-## Five things in this dialect that do not do what they look like
+## Five things that did not do what they looked like
 
-Each of these cost an evening, and each was filed in `TODO.md` §9 with a reduction and
-the file and line of the cause. **Three of the five have since been fixed**, and are kept
-here as the history of why this program is shaped the way it is — a listing whose
-comments explain what it was avoiding is worth more than one quietly rewritten to pretend
-the problem never existed. The two that remain are the first and the last, and the first
-is the dangerous one.
+Each cost an evening, and each was filed in `TODO.md` §9 with a reduction and the file
+and line of the cause. **Three of the five have since been fixed** — the interpreter
+changed, not the game — and they are kept here because the shape of the program is still
+theirs: a listing whose comments explain what it was avoiding is worth more than one
+quietly rewritten to pretend the problem never existed.
+
+**Two still stand, and they are the first two.** Read those; the rest is history.
 
 ### 1. The left operand decides integer or float arithmetic