Move to the layout REPO_POLICIES.md gives (closes #30)

The Go module moves from backend/ to the root (go.mod, go.sum,
.golangci.yml, cmd/, internal/), the page's source to web/, and nginx's
two files to configs/. backend/ is gone: its LICENSE and .dockerignore
are deleted, and its .gitignore entries, README and scripts are folded
into the root ones. script/build builds the server binary after the
frontend; script/run and script/clean move up from backend/script/;
make test, lint, fmt and fmt-check do what the backend's did. Vite's
root is web/ and it still builds into dist/. script/bootstrap no longer
installs gcc, which only the host Go tests needed.

Model: opus-5-5

script/frontend-fmt

@@ -1,9 +1,9 @@
 #!/bin/sh
 # script/frontend-fmt: format the JavaScript, CSS, HTML and Markdown,
-# repo-wide (writes), the markdown in backend/ included. Those are the
-# languages REPO_POLICIES.md gives prettier; the YAML is left alone, as
-# backend/.golangci.yml must stay the org standard byte for byte.
-# Prettier does not read Go; backend/script/fmt formats the Go sources.
+# repo-wide (writes). Those are the languages REPO_POLICIES.md gives
+# prettier; the YAML is left alone, as .golangci.yml must stay the org
+# standard byte for byte. Prettier does not read Go; script/fmt runs
+# gofmt over the Go sources.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"