Format Markdown with prettier in script/fmt and script/fmt-check (refs #7)

script/fmt now also runs prettier over every Markdown file, and
script/fmt-check checks them without writing. prettier is pinned in
package.json and yarn.lock. script/bootstrap keeps its Go and apt
handling and gains the canonical pinned node (nvm from a hash-checked
archive) and yarn (corepack) install, then installs the locked
packages. Both fmt scripts find yarn the canonical way, sourcing nvm
when yarn is not on PATH. The new files and the yarn lookup come from
sneak/prompts at cc440118c876. The vendored REPO_POLICIES.md already
passes prettier, so it is not ignored. The Markdown is reformatted in
the next commit.

Deviation: package.json drops the canonical "license": "MIT" line; this
repo is WTFPL.

Model: opus-5-5

TODO.md

@@ -20,6 +20,10 @@ v2.14.0 in the same commit, and fix the findings it surfaces
 
 # Completed Steps
 
+- 2026-10-06: Formatted Markdown with prettier: `script/fmt` writes and
+  `script/fmt-check` checks every Markdown file; prettier pinned in
+  `package.json` and `yarn.lock`, installed by `script/bootstrap` with a
+  pinned node and yarn; existing Markdown reformatted.
 - 2026-10-05: Brought the repo up to the standard layout: canonical
   `.gitignore`, `.dockerignore` and `.editorconfig`; `lint` and `test`
   phases in the `Dockerfile`, built by `script/lint` and `script/test`;
@@ -41,8 +45,6 @@ v2.14.0 in the same commit, and fix the findings it surfaces
 
 # Future Steps
 
-- Format Markdown with prettier in `script/fmt` and `script/fmt-check`
-  (https://git.eeqj.de/sneak/bsdaily/issues/7).
 - Expand tests beyond the compilation smoke test: unit tests for the
   extraction, verification, and atomic-publish paths.
 - Cut a first SemVer release once compliance and test coverage land.