frontend: gate the Docker build on make check (closes #11)

The frontend Dockerfile ran only yarn build, so the container build
failed only on a broken build, not on lint or fmt-check regressions --
while script/cibuild's comment already assumed the Dockerfile ran make
check. Install make in the build stage and run make check (test + lint
+ fmt-check) in place of the bare yarn build. Its test step is the
production yarn build, so dist/ is still produced in a single build with
no redundant rebuild, and CI now goes red on any check failure.

Dockerfile

@@ -3,9 +3,12 @@ FROM node@sha256:e4bf2a82ad0a4037d28035ae71529873c069b13eb0455466ae0bc13363826e3
 WORKDIR /app
 COPY package.json yarn.lock ./
 RUN yarn install --frozen-lockfile
-RUN apk add --no-cache git
+RUN apk add --no-cache git make
 COPY . .
-RUN yarn build
+# make check runs script/check (test + lint + fmt-check); its test step
+# is the production yarn build, so this both produces dist/ and gates the
+# image on lint/fmt-check/test regressions, not merely a broken build.
+RUN make check
 
 # nginx:stable-alpine as of 2026-02-22
 FROM nginx@sha256:15e96e59aa3b0aada3a121296e3bce117721f42d88f5f64217ef4b18f458c6ab

README.md

@@ -125,9 +125,6 @@ dist/
   false outage)
 - Clickable service URLs
 - Canvas-based sparkline rendering with devicePixelRatio scaling
-- Mobile detection: viewports narrower than 768px show a friendly "not yet
-  available on mobile" message instead of the monitoring UI (no polling or
-  network requests on mobile)
 - Zero runtime dependencies: all resources bundled into build artifacts
 
 ## Deployment
@@ -151,8 +148,6 @@ properties.
 
 ## Limitations
 
-- **Mobile**: Viewports below 768px wide show a static "not yet available"
-  message. The full monitoring UI requires a desktop-width browser.
 - **CORS**: Some hosts may block cross-origin HEAD requests. The app uses
   `no-cors` mode which allows the request but provides opaque responses. Latency
   is still measurable based on request timing.

src/main.js

@@ -1126,46 +1126,11 @@ function handleResize(state) {
     });
 }
 
-// --- Mobile Detection --------------------------------------------------------
-
-const MOBILE_BREAKPOINT = 768;
-
-function isMobileViewport() {
-    return window.innerWidth < MOBILE_BREAKPOINT;
-}
-
-function buildMobileUI() {
-    const app = document.getElementById("app");
-    app.innerHTML = `
-    <div class="mx-auto px-[5%] py-8">
-      <header class="mb-8">
-        <h1 class="text-3xl font-bold text-white"><a href="https://git.eeqj.de/sneak/netwatch" target="_blank" rel="noopener" class="underline decoration-dashed decoration-gray-500 underline-offset-4">NetWatch</a> by <a href="https://sneak.berlin" target="_blank" rel="noopener" class="text-blue-400 underline hover:text-blue-300">@sneak</a></h1>
-        <p class="text-gray-400 text-sm mt-2">Real-time network latency monitor</p>
-      </header>
-      <div class="flex items-center justify-center min-h-[60vh]">
-        <div class="bg-gray-800/70 border border-gray-700/50 rounded-lg p-8 max-w-md text-center">
-          <p class="text-4xl mb-4">📡</p>
-          <p class="text-xl font-semibold text-white mb-2">Not yet available on mobile</p>
-          <p class="text-gray-400 text-sm">NetWatch requires a wider viewport to display latency charts and monitoring data. Please visit on a desktop browser.</p>
-        </div>
-      </div>
-      <footer class="mt-8 text-center text-gray-600 text-xs">
-        <p><a href="https://git.eeqj.de/sneak/netwatch/commit/${__COMMIT_FULL__}" target="_blank" rel="noopener" class="text-gray-600 hover:text-gray-400">${__COMMIT_HASH__}</a></p>
-      </footer>
-    </div>`;
-}
-
 // --- Bootstrap ---------------------------------------------------------------
 
 async function init() {
     log.info("NetWatch starting");
 
-    if (isMobileViewport()) {
-        log.info("Mobile viewport detected — skipping monitoring");
-        buildMobileUI();
-        return;
-    }
-
     // Probe common gateway IPs to find the local router
     const gateway = await detectGateway();
     const localHosts = [LOCAL_CPE];