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/. go.mod ignores
node_modules/, whose npm packages can ship .go files. script/bootstrap
no longer installs gcc, which only the host Go tests needed.

Model: opus-5-5

test/viewport/README.md

@@ -7,11 +7,11 @@ make frontend-viewport-test
 ```
 
 It builds `dist/`, serves it from the same digest-pinned `nginx` image and the
-same `nginx.conf` the shipping container uses, drives a digest-pinned headless
-Chrome against it over CDP, and asserts on computed layout at every viewport
-width derived from the app's own CSS. Screenshots land in `tmp/viewport/`
-alongside a `results.json`; they are artifacts for a human to look at when
-something fails, not the evidence. The assertions are the evidence.
+same `configs/nginx.conf` the shipping container uses, drives a digest-pinned
+headless Chrome against it over CDP, and asserts on computed layout at every
+viewport width derived from the app's own CSS. Screenshots land in
+`tmp/viewport/` alongside a `results.json`; they are artifacts for a human to
+look at when something fails, not the evidence. The assertions are the evidence.
 
 The target is deliberately outside `make check`: it takes minutes, and
 `make test` has to stay under 60 seconds.
@@ -19,10 +19,10 @@ The target is deliberately outside `make check`: it takes minutes, and
 ## How the widths are chosen
 
 Not from a list of phone models. `viewports.js` parses the `@media` conditions
-out of `src/styles.css` and scans `src/main.js` and `index.html` for Tailwind
-responsive prefixes, then tests every breakpoint it finds at one pixel below it,
-exactly on it, and one pixel above it. A generic 375px "phone" test sails
-straight past an off-by-one at a media query boundary; `max-width: 768px`
+out of `web/src/styles.css` and scans `web/src/main.js` and `web/index.html` for
+Tailwind responsive prefixes, then tests every breakpoint it finds at one pixel
+below it, exactly on it, and one pixel above it. A generic 375px "phone" test
+sails straight past an off-by-one at a media query boundary; `max-width: 768px`
 matches _at_ 768, and the sweep pins down which side of that line each layout is
 on.
 
@@ -108,7 +108,7 @@ function of viewport width and CSS, and is covered above.
 
 Complementary layers, not two stacks. The unit tests in `test/unit/`, which
 `make test` runs with Node's built-in test runner, exercise the functions
-`src/main.js` exports in-process with no browser. This harness exercises
+`web/src/main.js` exports in-process with no browser. This harness exercises
 rendered layout in a real engine and is the only thing here that can see a media
 query. Neither replaces the other; assertions about computed styles and element
 geometry belong here, assertions about functions belong in `test/unit/`.