Bring the tutorials back in line with the fixed interpreter

Eleven of the thirteen defects these two games found are fixed, and the
chapters that taught around them said things that are no longer true.

Chapter 17: the drawing verbs are no longer invisible, they are covered by a
text layer that `WINDOW` can now shrink; the cell size is `RGR(3)` and the grid
is `RWINDOW`, not a hand-measured constant; a character written past a short
row's end lands. Chapter 18: traps 3 and 4 -- the skipped block that broke its
caller's `RETURN`, and `SSHAPE` ignoring a subscript -- become history rather
than warnings, and Step 3 no longer claims a sprite is the *only* way to put a
picture up, only the one that costs nothing.

**Neither `.bas` listing changes, and both READMEs now say why.** The character
game still writes `CW# = 16` and the artwork game still keeps six brick stamps
in six scalars. What those listings are worth is being what a program written
against those constraints looks like, with comments explaining what each one was
avoiding -- rewriting them to pretend the problems never existed would throw
that away. So Chapter 17 Step 2 shows the `RGR(3)`/`RWINDOW` form and says
plainly that the listing beside it does not use it. That is the one place in
either chapter where a quoted fragment is not verbatim from the game.

Also: the closing pointers now say which entries are struck and which stand, and
the budgets table in Chapter 18 notes that several of those budgets were tighter
when the game was written.

TODO.md section 9 item 3 is updated rather than struck: the `WINDOW` half is
fixed, the default text area owning the whole window is not, and whether that
default is right is a question rather than a defect.

Verified against the fixed interpreter: both games run 45 seconds on the SDL
frontend with no error line and the score climbing; both suites are green in
both configurations; `docs_examples` passes and `docs_screenshots --check`
re-renders all thirteen figures byte-identically; coverage is 95.0% of lines
against the 90 gate, with src/variable.c at 100%; and every other quoted
fragment still appears verbatim in the listing it came from.

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

examples/breakout/sprites/README.md

@@ -68,9 +68,9 @@ Crediting Kenney is not required by CC0. It is here because it should be.
 Named honestly rather than left to be discovered:
 
 - **No music under the game**, only event sounds and two four-note stings. There is room in
-  the third voice for it; there is not much room anywhere else. 121 of the interpreter's
-  128 variables are spoken for, four more are the ones it makes itself, and the label table
-  is at 61 of 64.
+  the third voice for it; there was not much room anywhere else when it was written. 121 of
+  the interpreter's 128 variables are spoken for and the label table is at 61 of 64 —
+  several of them spent working around defects that have since been fixed.
 - **One gem at a time.** There is one sprite slot for it. A brick broken while a gem is
   falling drops nothing.
 - **Sticky and multiball share one offset.** Two balls stuck to the paddle at once sit on
@@ -82,5 +82,13 @@ Named honestly rather than left to be discovered:
 - **No high score on disk.** There is no disk.
 
 The eight interpreter defects this game turned up are filed in `TODO.md` §9, each with a
-reduction that fits on a screen, the file and line of the cause, and what a fix would
-touch.
+reduction that fits on a screen and the file and line of the cause. **Six are now fixed**
+— the leaking `DEF` call, the skipped block that broke its caller's `RETURN`, the ignored
+subscript on `SSHAPE`, `GRAPHIC CLR`, a negative `DATA` item, and half of the invisible
+drawing. The two that stand are the left-operand arithmetic rule, which turned out to be a
+decision rather than a defect and is now documented as one, and the 256-line batch tear,
+which belongs to the host.
+
+**The listing is unchanged**, and deliberately: it is what a program written against those
+constraints looks like, and its comments explain what it was working around. Six separate
+scalars for six brick stamps is no longer necessary, and it is still what the file does.