Extract Alpine.js in script/test so the pre-commit hook works

The extraction moves from the Makefile's assets target into
script/assets. script/test runs it before the tests, so make test,
make check, script/check and the pre-commit hook all get the file on a
fresh clone; make assets, make build and make dev call the same script.
The README now says only that nothing downloads Alpine.js.

Model: opus-5-5

README.md

@@ -1247,16 +1247,16 @@ What that means for an operator:
 This repository adheres to the
 [Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
 standard: normalized scripts in `script/` are the entrypoints for the
-development workflow. Nine of the Makefile's seventeen targets are thin
-shims that call them; `assets`, `build`, `run`, `dev`, `deps`, `clean`,
-`css` and `version` are inline commands with no script behind them,
-though `build` and `version` both take their value from
-`script/version`.
+development workflow. Ten of the Makefile's seventeen targets are thin
+shims that call them; `build`, `run`, `dev`, `deps`, `clean`, `css` and
+`version` are inline commands with no script behind them, though `build`
+and `version` both take their value from `script/version`.
 
-`make test`, `make check`, `make build` and `make dev` each run
-`make assets` first, which writes the ignored `static/js/alpine.min.js`
-(see [Third-party browser assets](#third-party-browser-assets)), so
-`make check` works on a fresh clone without a separate setup step.
+`script/test`, `make build` and `make dev` each run `script/assets`
+first, which writes the ignored `static/js/alpine.min.js` (see
+[Third-party browser assets](#third-party-browser-assets)), so
+`make test`, `make check` and the pre-commit hook work on a fresh clone
+without a separate step.
 
 We provide:
 
@@ -1264,6 +1264,8 @@ We provide:
 - `script/setup` — make a fresh clone ready for development
   (bootstrap, then install-precommit)
 - `script/projectname` — output the project name ("webhooker")
+- `script/assets` — extract Alpine.js from its tarball in `3p/` (see
+  [Third-party browser assets](#third-party-browser-assets))
 - `script/test` — run the test suite
 - `script/lint` — run golangci-lint in Docker (see Linting below)
 - `script/fmt` — format all code (writes)
@@ -1292,19 +1294,18 @@ publishes it. It is a dependency, not this repo's build output, so
 The directory is `3p/` rather than `vendor/` because Go treats a root
 `vendor/` directory as its module vendor directory.
 
-`make assets` extracts the browser build, `package/dist/cdn.min.js`, from the
-tarball to `static/js/alpine.min.js`, where `go:embed` picks it up.
-`make test`, `make check`, `make build` and `make dev` run it first, and the
-Dockerfile builds through them, so no build downloads anything. The extracted
-file is not committed, and `.dockerignore` keeps any host copy out of the
-build context.
+`script/assets` (`make assets`) extracts the browser build,
+`package/dist/cdn.min.js`, from the tarball to `static/js/alpine.min.js`,
+where `go:embed` picks it up. `script/test`, `make build` and `make dev` run
+it first, and the Dockerfile builds through `make test` and `make build`, so
+nothing downloads Alpine.js. The extracted file is not committed, and
+`.dockerignore` keeps any host copy out of the build context.
 
 To move to a new version: download
 `https://registry.npmjs.org/alpinejs/-/alpinejs-<version>.tgz`, check it
 against the `dist.integrity` hash listed at
 `https://registry.npmjs.org/alpinejs/<version>`, replace the tarball in `3p/`
-with it, update its file name in the Makefile's `assets` target, and run
-`make check`.
+with it, update its file name in `script/assets`, and run `make check`.
 
 ## Rationale
 
@@ -2883,7 +2884,7 @@ webhooker/
 ├── script/                    # Scripts to Rule Them All entrypoints
 ├── Dockerfile                 # Three stages: lint, test+build, Alpine runtime
 ├── Dockerfile.lint            # Lint-only image built by script/lint
-├── Makefile                   # 9 of 17 targets shim script/; 8 are inline
+├── Makefile                   # 10 of 17 targets shim script/; 7 are inline
 ├── go.mod / go.sum
 └── .golangci.yml              # Linter configuration
 ```