Shim make dev and make build, format backend/ markdown (closes #28)

make dev ran yarn dev inline and there was no make build. Both are now
shims, over script/dev and the new script/build. .prettierignore stops
leaving out backend/, so backend/README.md is formatted and checked;
backend/.golangci.yml is left out by name instead: it is the org
standard file whose sha256 backend/script/lint checks, and prettier
would reindent it. .claude/ stays in .prettierignore, as git does not
ignore it. script/install-precommit and the date on bootstrap's pins go
back to the org model; bootstrap, fmt and fmt-check keep what the Go
backend and eslint need, each with a comment saying so.

Model: opus-5-5

script/bootstrap

@@ -17,11 +17,13 @@
 #
 # golangci-lint is not installed: make lint runs it in Docker, which
 # this script does not install either.
+#
+# Unlike the org model: Go and gcc for backend/, a newer node for eslint.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned versions, 2026-07-07
+# Pinned versions, 2026-07-06
 NODE_VERSION="22.17.0"
 # The oldest node the frontend's dependencies accept: the "engines"
 # field of eslint 10.12.0, the most demanding of them, asks for 22.13.0