Add the sign-up page and the first-run checklist

Second half of #7. The API could create accounts from invite links since
the last change; this is the part somebody can actually use.

/signup is the one route that works without a session. It asks the server
what it may offer before showing anything: an invite link that is good
names the team it leads to, a link that is not says so before somebody
picks a password rather than after, and an invite-only server with no
link says that instead of presenting a form it will refuse. The login
card only offers "create one" when sign-up is open, so the door nobody
can walk through is not advertised.

Signing up signs you in and lands on the queue, because the alternative
is a form saying "now go and log in" about the credential just chosen.

The checklist is the other half. Four things have to be true before an
alert reaches a phone -- a notification topic, somebody on the rota, an
alert source, and an alert that has actually arrived -- and on a fresh
install none of them are. It sits above the queue until they are.

It is computed from the data rather than from stored progress: a topic is
set or it is not, an integration exists or it does not. That means it
cannot claim a step is done when it is not, and it comes back by itself
if somebody deletes their integration a month later. The only stored
state is the dismissal, which is per user and not per browser --
finishing on a laptop should not leave the phone nagging.

The topic step is the only one the checklist can finish itself, and the
only proof that counts is a phone buzzing, so there is a test push.
POST /api/me/notify/test publishes directly rather than through the
outbox, which requires an incident this deliberately does not have. Its
failure is the useful part: a wrong topic, a rejected token and an ntfy
that is down all look identical from the phone, which is silence, so the
error comes back to the browser instead.

Verified against a live server with a real ntfy stand-in, the whole path:
an owner mints an invite, the sign-up page reports it valid and names the
team, the invitee signs up and is signed in as a member of that team, the
checklist's four questions answer correctly on a fresh install, a test
push is refused with no topic and delivered with one -- "PAGED
terdut-owner | terdut test" -- and the dismissal survives a reload.

Claude-Session: https://claude.ai/code/session_01RHPj4ggeFdEjKKfm4SHbD7

internal/web/static/js/onboarding.js

@@ -0,0 +1,147 @@
+// The first-run checklist: the four things a new install or a new person has
+// to do before an alert reaches a phone.
+//
+// It is computed from what the server already knows rather than from stored
+// progress — a topic is set or it is not, an integration exists or it does not
+// — so it cannot claim a step is done when it is not, and it comes back by
+// itself if somebody deletes their integration a month later.
+//
+// Dismissal is the one piece of state, kept per user so finishing on a laptop
+// does not leave the phone nagging.
+
+import * as api from './api.js';
+import { h, clear, spinner } from './ui.js';
+import { state, currentTeam } from './state.js';
+import { navigate } from './app.js';
+import { isoDate } from './format.js';
+
+let steps = null;
+let error = null;
+let busy = false;
+let testResult = null;
+
+// done() is deliberately a question about the world, not a flag: each step asks
+// the data whether it happened.
+export async function load() {
+  const team = currentTeam();
+  if (!team) {
+    steps = null;
+    return;
+  }
+  try {
+    const [schedule, integrations, alerts] = await Promise.all([
+      api.schedule(team.id, isoDate(new Date()), isoDate(new Date())),
+      api.integrations(team.id),
+      api.alerts({ limit: 1 }),
+    ]);
+    steps = [
+      {
+        id: 'topic',
+        title: 'Set where your pages go',
+        text: 'An ntfy topic on your account. Without one, incidents assigned to you page the team’s fallback topic instead of your phone.',
+        done: Boolean(state.me?.user?.ntfy_topic),
+        action: { label: 'Account', go: '/more' },
+      },
+      {
+        id: 'rota',
+        title: 'Put somebody on call',
+        text: 'An incident opens assigned to whoever the rota says is on call today. With an empty rota it opens unassigned.',
+        done: (schedule || []).length > 0,
+        action: { label: 'Team', go: '/team' },
+      },
+      {
+        id: 'integration',
+        title: 'Create an alert source',
+        text: 'Alerts arrive on an integration key, which says which team they belong to. Nothing can reach this team without one.',
+        done: (integrations || []).length > 0,
+        action: { label: 'Team', go: '/team' },
+      },
+      {
+        id: 'alert',
+        title: 'Send a test alert',
+        text: 'Post to the integration URL and watch it appear in the queue. Until one arrives, none of the above is proven.',
+        done: (alerts || []).length > 0,
+        action: { label: 'How', go: '/team' },
+      },
+    ];
+    error = null;
+  } catch (err) {
+    error = err.message;
+  }
+}
+
+// visible reports whether there is anything worth showing: something undone,
+// and not dismissed.
+export function visible() {
+  if (!steps || state.me?.onboarding_dismissed) return false;
+  return steps.some((s) => !s.done);
+}
+
+export function card() {
+  if (!visible()) return null;
+  const remaining = steps.filter((s) => !s.done).length;
+
+  return h('div', { class: 'card onboarding' },
+    h('div', { class: 'onboarding-head' },
+      h('h2', { text: 'Finish setting up' }),
+      h('span', { class: 'muted small', text: `${remaining} left` }),
+      h('button', {
+        class: 'btn-sm', type: 'button', text: 'Hide',
+        title: 'Hide this checklist for good',
+        onclick: async () => {
+          try {
+            await api.dismissOnboarding(true);
+            if (state.me) state.me.onboarding_dismissed = true;
+          } catch (err) {
+            error = err.message;
+          }
+          rerender();
+        },
+      })),
+    error && h('p', { class: 'load-error', text: error }),
+    h('ol', { class: 'checklist' }, ...steps.map(stepRow)),
+    testResult && h('p', { class: testResult.ok ? 'muted small' : 'load-error', text: testResult.text }),
+  );
+}
+
+function stepRow(step) {
+  return h('li', { class: step.done ? 'step done' : 'step' },
+    h('span', { class: 'step-mark', text: step.done ? '✓' : '' }),
+    h('div', {},
+      h('strong', { text: step.title }),
+      h('p', { class: 'muted small', text: step.text }),
+      !step.done && h('div', { class: 'step-actions' },
+        h('button', {
+          class: 'btn-sm', type: 'button', text: step.action.label,
+          onclick: () => navigate(step.action.go),
+        }),
+        // The topic step is the only one this page can finish by itself, and
+        // the only proof that matters is a phone buzzing.
+        step.id === 'topic' && state.me?.user?.ntfy_topic && h('button', {
+          class: 'btn-sm', type: 'button', text: 'Send a test push',
+          disabled: busy,
+          onclick: sendTest,
+        }),
+      )),
+  );
+}
+
+async function sendTest() {
+  busy = true;
+  try {
+    await api.testNotification();
+    testResult = { ok: true, text: 'Sent. If nothing arrives, the topic is wrong or ntfy is not reachable.' };
+  } catch (err) {
+    testResult = { ok: false, text: err.message };
+  } finally {
+    busy = false;
+  }
+  rerender();
+}
+
+// The queue owns the card's place on the page, so ask it to redraw rather than
+// reaching into its list.
+let rerender = () => {};
+export function onRerender(fn) {
+  rerender = fn;
+}