make fmt and make fmt-check cover Markdown with prettier (closes #39)

make fmt and make fmt-check now cover the Markdown files with prettier as well as the Go source: prettier 3.8.1 pinned in package.json and yarn.lock, four-space indents and proseWrap always in .prettierrc, all three copied unchanged from the sneak/prompts templates. script/bootstrap adds pinned node (through nvm from a hash-checked archive when none is installed), yarn and prettier after the pinned Go. README.md is reformatted by make fmt and its Entrypoints section says what each step needs.

Model: opus-5-5

.prettierrc

@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}