Rewrite the two game tutorials as instructions rather than commentary

Chapters 17 and 18 read as a code review of a finished listing: they explained
why each decision had been made, walked through the project's own history, and
led with what had once been broken. A reader who wanted to build the game got
the reasoning and had to reconstruct the program.

Both are now step-by-step. Each opens with a picture of the finished game and a
bullet list of the steps, each bullet is a section, and each section states its
goal, shows the code, and says how to check it. Chapter 17 is sixteen steps and
Chapter 18 is thirteen, and the last of each is the assembly: the order of the
file, the full declaration block, and the routines the earlier steps referred to.
Project history is gone -- it belongs in Chapter 14 and in git -- and where a
listing has to do something awkward, the tutorial shows how first and names the
`TODO.md` item that will make it unnecessary second.

**Three defects had no entry anywhere**, which the rewrite found by trying to
state each rule as a rule. §6 item 35: `a - b + c` computes `a - (b + c)`,
because `subtraction()` sits above `addition()` as its own precedence level and
the inner loop eats the `+`. Item 36: only one unparenthesised `AND` or `OR` is
matched, which is item 12's `if`-where-`while` on the one operator pair item 12
did not reach. Item 37: a `GOTO` out of a `FOR` or a `DO` leaks the loop's scope,
so a main loop written that way stops on the thirty-second lost life -- which is
why both games are built out of `LABEL` and `GOTO`, and it is a workaround rather
than a preference. Chapter 3 gains the identifier rule the third trial ran into:
there is no underscore in a name, and the error says `UNKNOWN TOKEN _`.

**`tools/screenshot.c` learned to draw the text layer**, behind a new `text=1`
fence attribute, because Chapter 17's game is characters in the grid and a figure
without that layer is two sprites on black. It opens the bundled font at the size
the standalone frontend uses, so a figure's cell size is the reader's cell size,
and it uses the akgl sink alone rather than a tee so the program's output lands in
the picture instead of on the stdout the caller reads to decide a figure failed.
Both new figures -- `breakout-game.png` and `breakout-game-artwork.png` -- are
generated from listings in the chapters like every other one.

Verified by handing each chapter, alone, to an agent on a much smaller model and
telling it to build the game from the tutorial text with the `examples/` tree off
limits. The first pass scored 3.5 and 3 out of 10 and named what was missing:
routines referred to but never shown, the third level layout, the sprite `DATA`,
the font table, edits to earlier routines that were never marked as edits. Those
are now in. The second pass built a 658-line Chapter 17 game that plays itself
for ninety seconds with the score at 1890 and no error line, and the third built
a 1053-line Chapter 18 game with 61 labels, no invented routines, no gaps found,
and forty seconds clean. 9/10 and 8/10.

One real bug in the new prose, caught in review: Chapter 18's `HITBAR` did not
set the `HIT#` that `BALLPADDLE` reads to decide whether the paddle already
caught the ball. Both suites green in both configurations, `docs_examples` and
`docs_screenshots --check` pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL

MAINTENANCE.md

@@ -611,6 +611,7 @@ a missing decision rather than a free pass.
 | `text` | **Never executed.** A block diagram, or a stack trace captured from a real run |
 | `basic screenshot=NAME` | Also the source of `docs/images/NAME.png`. The harness checks the file exists; `tools/docs_screenshots.sh` is what makes it |
 | `basic size=WxH` | That figure's surface, when 320x200 is not the size the point needs |
+| `basic text=1` | That figure is drawn **with** the text layer, for a program whose output is characters |
 
 Attributes combine: `basic requires=akgl setup=ship` is a real tag in `docs/08-sprites.md`.
 
@@ -627,8 +628,18 @@ $ cmake --build build-akgl --target docs_screenshots
 
 `tools/screenshot.c` is a second, much smaller SDL host — the dummy video driver, a
 software renderer, run the program to completion, read the target back, write a PNG. It
-draws no text layer, deliberately: a `READY` in the corner is noise in a figure about
-`BOX`, and skipping it means no font has to be found.
+draws no text layer by default, deliberately: a `READY` in the corner is noise in a figure
+about `BOX`, and skipping it means no font has to be found.
+
+**`text=1` turns the text layer on**, for the case that default gets wrong: a figure of a
+program whose output *is* characters. `docs/17-tutorial-breakout.md` builds a game whose
+wall, HUD and messages are all in the grid, and without the layer its figure is two sprites
+on a black field. The tag makes `docs_screenshots.sh` hand the tool
+`assets/fonts/C64_Pro_Mono-STYLE.ttf` at `AKBASIC_FRONTEND_FONT_SIZE`, which is what the
+standalone frontend opens, so the figure's cell size is the reader's cell size. The sink is
+then the akgl one *alone* rather than a tee, so the program's output goes into the picture
+instead of onto stdout — which the caller reads to decide a figure failed. A raised error
+is still caught, by `docs_examples` running the same block.
 
 Three rules around it: