docs: how to set up, run and publish this tree

The setup is unusual enough to need its own page, and the facts were
scattered across scratch.md, CLAUDE.md and publish.sh: the mod is developed
inside a copy of a commercial game, so the dev tree deliberately has no
remote and publishing means rebuilding a filtered repo and force-pushing
that instead.

docs/00-dev-setup.md covers the two-tree arrangement and which one you are
in, prerequisites and why the game must be an extracted folder rather than
a .love (ffi.load goes through the OS loader), building a dev tree from
scratch including the vanilla-0.4.2 baseline tag and the one main.lua line,
the everyday commands, the save location, reading the [speech] console and
the startup self-test, and the publish flow with its leak check.

Linked from CLAUDE.md and the docs index. No code change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

accessibility/docs/scratch.md

@@ -9,6 +9,9 @@ playtesting.** Remaining work is polish, mod settings and distribution.
 conversation into gameplay, plus journal, character, actions and inventory —
 verified by the testbed, **34/34 checks**.
 
+**Not set up yet, or unsure how the two trees relate?** →
+[00-dev-setup.md](00-dev-setup.md).
+
 ### Run the testbed (do this after any change)
 ```
 cd "D:/code/Sulphur Memories Alchemist 0.4.2 sanctified"