Add Setup: first farm, gateway settings, add and remove printers; show alerts

A new user could sign in and see an empty page with no way forward. Setup
walks them through it: create a farm (reusing their organisation if they
already have one); get the gateway settings with a freshly minted token,
shown once and removed from the page when dismissed, with a confirmation
first if a gateway is already connected, since minting replaces the old
token; add a Bambu printer by address, serial and access code (a printer
the gateway discovered fills the form in); remove a printer behind a named
confirmation that says it also deletes the stored credential.

The access code field is cleared after every submit, success or failure, and
the page says plainly that the code goes to the gateway and nowhere else.
Add is disabled while no gateway is connected, because the code has nowhere
to go.

The fleet page now lists open alerts above the printers (polled every 5s)
with a Dismiss button, and points an empty account at Setup.

Verified in real Chrome by scripts/e2e-setup-browser.sh in continuum-backend:
nothing -> farm -> gateway -> printer -> failed-print alert -> dismissed ->
removed, with no page errors.

apps/web/pages/index.vue

@@ -1,6 +1,8 @@
 <script setup lang="ts">
 import {
+  AlertList,
   FarmStatus,
+  type AppAlert,
   PrinterCard,
   type AppFarm,
   type AppFarmDiscovery,
@@ -70,12 +72,33 @@ async function refreshFarmStatus() {
   }
 }
 
+// What still needs a person. Polled on the same 5s beat as jobs: an alert is
+// useful for minutes, not milliseconds, and a push channel for it would be a
+// second socket to keep honest.
+const { data: alerts, refresh: refreshAlerts } = await useAsyncData("alerts", () =>
+  apiFetch<AppAlert[]>("/alerts", { query: { open: true } }),
+);
+
+async function acknowledge(id: string): Promise<void> {
+  try {
+    await apiFetch(`/alerts/${id}/acknowledge`, { method: "POST" });
+  } catch (err) {
+    throw new Error(apiErrorMessage(err, "could not dismiss the alert"));
+  }
+  await refreshAlerts();
+}
+
 let farmPoll: ReturnType<typeof setInterval> | undefined;
+let alertPoll: ReturnType<typeof setInterval> | undefined;
 onMounted(() => {
   void refreshFarmStatus();
   farmPoll = setInterval(() => void refreshFarmStatus(), 10_000);
+  alertPoll = setInterval(() => void refreshAlerts(), 5_000);
+});
+onBeforeUnmount(() => {
+  clearInterval(farmPoll);
+  clearInterval(alertPoll);
 });
-onBeforeUnmount(() => clearInterval(farmPoll));
 
 /**
  * Sends one command to a printer and turns a refusal into a sentence.
@@ -114,7 +137,11 @@ watch(
 <template>
   <div class="fleet">
     <h1>Fleet overview</h1>
+    <p v-if="farms && !farms.length">
+      You have no farm yet. <NuxtLink to="/setup">Set one up</NuxtLink> to connect your printers.
+    </p>
     <FarmStatus v-for="farm in farms ?? []" :key="farm.id" :farm="farm" :status="farmStatus[farm.id] ?? null" />
+    <AlertList :alerts="alerts ?? []" :acknowledge="acknowledge" />
     <div class="fleet__grid">
       <PrinterCard
         v-for="printer in printers ?? []"