Rewrite both tutorials as tutorials

They read as design commentary: why a choice was made, what the previous state
of the project was, which library defect a line works around. That is useful to
somebody who already knows the library and useless to somebody trying to build a
game, which is who a tutorial is for.

Both chapters now open with a screenshot of what the reader is building and a
numbered list of the steps to get there, and each step is its own section: what
you are trying to achieve, the code that achieves it, and the two or three things
about that code that are easy to get wrong. Chapter 20 starts from first
principles -- what a sprite, a character, an actor and a tilemap are, and the
four error macros -- and chapter 21 assumes it and covers what a top-down game
adds.

Where a line exists because of a defect, the line comes first and the defect
comes after it, with a pointer to the TODO entry that will remove the need. A
reader who is copying code should not have to read an apology before they can use
it.

The library's own history is gone from both. That belongs in the design chapters
and in git.

Two new docs_examples setups stage the tutorials' own art, so the sprite and
character files a reader is shown are loaded exactly as printed rather than
through a generic fixture. `json excerpt=` is new for the same reason: a Tiled
object is now quoted out of the real map instead of being retyped. Excerpts
across docs/ go from 91 to 137.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71

docs/README.md

@@ -32,13 +32,16 @@ per-function reference, build the Doxygen output with `doxygen Doxyfile`.
 | **[17. Text and fonts](17-text-and-fonts.md)** | Loading, drawing, measuring, and the teardown order that matters |
 | **[18. Audio](18-audio.md)** | The three-voice synthesizer, and the separate background-music path |
 | **[19. Utilities](19-utilities.md)** | Rectangle overlap, path resolution, the JSON accessors, static strings |
-| **[20. Tutorial: a 2D sidescroller](20-tutorial-sidescroller.md)** | Gravity, a jump, collision, coins and hazards |
-| **[21. Tutorial: a top-down JRPG](21-tutorial-jrpg.md)** | A town map, NPCs spawned from map objects, four-way animation, a text box, a follower |
+| **[20. Tutorial: a 2D sidescroller](20-tutorial-sidescroller.md)** | Thirteen steps from an empty directory to a game with gravity, a jump, coins and hazards. **Start here** |
+| **[21. Tutorial: a top-down JRPG](21-tutorial-jrpg.md)** | Thirteen more, for four-way movement, NPCs, a text box, a follower, and freezing the world |
 | **[22. Appendix](22-appendix-limits.md)** | Every limit, every status, every configuration property |
 
-Both tutorials are complete programs under [`examples/`](../examples). They build with the
-library and run headless in CI, and the chapters quote them rather than restating them — so
-a tutorial cannot drift from a program that compiles.
+**If you are new, read chapter 20 first and read it in order.** It builds a working game from
+an empty directory and teaches the library as it needs each piece; chapter 21 assumes it.
+Both are complete programs under [`examples/`](../examples) — they build with the library and
+run headless in CI, and the chapters quote them rather than restating them, so a tutorial
+cannot drift from a program that compiles. The picture at the top of each chapter is a frame
+out of the game itself, regenerated by `cmake --build build --target docs_game_figures`.
 
 ## Every example here is checked