Serve a web UI for the incident queue, built for phones

Whoever is on call gets paged on a phone, and until now the only ways to
act on a page were the notification's Acknowledge button or a terminal.
Tapping the notification itself opened /api/incidents/{id}, which a
browser can only answer with a 401 in JSON. The server now serves a web
UI at / covering the incident queue, each incident's alerts and timeline
with every action on it, who is on call, the alert feed, and changing
your own password. The notification link now points at /incidents/{id}
in that UI.

It is embedded in the binary and has no build step: plain HTML, CSS and
ES modules under internal/web/static, served with an ETag per file and a
CSP that allows nothing from any other origin. That is how rd-web is
built. It avoids adding a node toolchain to the Dockerfile and the
pipeline for a page this size, and it keeps the page on the same origin
as the API, so no CORS is needed and nothing else has to be deployed.
Paths without a file extension fall back to index.html, so a deep link
survives a reload. An unknown path under /api/ still gets a JSON 404
rather than the page.

Signing in uses a username and password, because pasting a 64-character
API key into a phone at 3am is not a sign-in flow. Users have no
password until one is set through PUT /api/users/{id}/password, or
optionally at bootstrap. A user without a password is exactly where they
were before this commit and can only use API keys. A login sets an
HttpOnly, SameSite=Lax session cookie. It lasts 30 days and slides
forward while in use, so an on-call phone does not sign itself out.
Only the token's hash is stored, as for API keys.

The cookie needs a CSRF guard where a bearer header does not, because
browsers attach cookies to requests other sites make. So cookie-
authenticated requests go through Go 1.25's http.CrossOriginProtection,
and bearer requests do not. A request carrying an Authorization header
is judged on that header alone and never falls back to the cookie.
Changing a password ends every other session of that user. Changing
your own requires the current password, so a phone left signed in
cannot be used to take the account over.

Failed logins are counted per username and per client address. Ten
failures for one username in 15 minutes refuse that username for the
rest of the window, even with the right password. That makes locking
somebody out possible for anyone who knows their username. It was
accepted because the alternative is unlimited guessing, and during a
lockout the notification's Acknowledge button and API keys keep
working. The address limit reads the first X-Forwarded-For hop, since
behind the gateway RemoteAddr is Envoy. It is looser, because a whole
office behind one NAT shares it.

The Secure flag follows TERDUT_PUBLIC_URL, since TLS terminates at the
gateway and the server itself only ever sees plain HTTP. The chart
already defaults that variable to https://<hostname>.

Schedule editing, statistics and user management stay in terdut-tui for
now. The API they use is unchanged, and bearer authentication behaves
exactly as before.

internal/web/static/js/api.js

@@ -0,0 +1,98 @@
+// The terdut-server client. The page is served by the server itself, so every
+// call is same-origin and carries the session cookie.
+
+export class ApiError extends Error {
+  constructor(status, message) {
+    super(message);
+    this.name = 'ApiError';
+    this.status = status;
+  }
+}
+
+// Called whenever the server says the session is gone, so the app can put the
+// login form back up wherever the user happened to be.
+let onUnauthorized = () => {};
+export function setUnauthorizedHandler(fn) {
+  onUnauthorized = fn;
+}
+
+async function call(method, path, { query, body, signal } = {}) {
+  const url = new URL('/api' + path, location.origin);
+  for (const [k, v] of Object.entries(query || {})) {
+    if (v === '' || v == null) continue;
+    url.searchParams.set(k, v);
+  }
+
+  const headers = { Accept: 'application/json' };
+  if (body !== undefined) headers['Content-Type'] = 'application/json';
+
+  let resp;
+  try {
+    resp = await fetch(url, {
+      method,
+      headers,
+      body: body === undefined ? undefined : JSON.stringify(body),
+      credentials: 'same-origin',
+      signal,
+    });
+  } catch (err) {
+    if (err.name === 'AbortError') throw err;
+    throw new ApiError(0, 'Cannot reach the server.');
+  }
+
+  if (resp.status === 204) return null;
+
+  let data = null;
+  try {
+    data = await resp.json();
+  } catch {
+    /* non-JSON body: keep null */
+  }
+
+  if (!resp.ok) {
+    if (resp.status === 401 && path !== '/login') onUnauthorized();
+    const message = (data && data.error) || `Server answered ${resp.status}.`;
+    throw new ApiError(resp.status, message);
+  }
+  return data;
+}
+
+// session
+export const me = () => call('GET', '/me');
+export const login = (username, password) => call('POST', '/login', { body: { username, password } });
+export const logout = () => call('POST', '/logout');
+export const setPassword = (userID, password, currentPassword) =>
+  call('PUT', `/users/${userID}/password`, { body: { password, current_password: currentPassword } });
+
+// users
+export const users = () => call('GET', '/users');
+
+// incidents
+export const incidents = (query, opts) => call('GET', '/incidents', { query, ...opts });
+export const incident = (id) => call('GET', `/incidents/${id}`);
+export const timeline = (id) => call('GET', `/incidents/${id}/timeline`);
+
+export const acknowledge = (id) => call('POST', `/incidents/${id}/acknowledge`);
+export const unacknowledge = (id) => call('DELETE', `/incidents/${id}/acknowledge`);
+export const resolve = (id) => call('POST', `/incidents/${id}/resolve`);
+export const assign = (id, userID) => call('POST', `/incidents/${id}/assign`, { body: { user_id: userID } });
+export const snooze = (id, spec) => call('POST', `/incidents/${id}/snooze`, { body: spec });
+export const unsnooze = (id) => call('DELETE', `/incidents/${id}/snooze`);
+export const archive = (id) => call('POST', `/incidents/${id}/archive`);
+export const unarchive = (id) => call('DELETE', `/incidents/${id}/archive`);
+export const addNote = (id, content) => call('POST', `/incidents/${id}/notes`, { body: { content } });
+export const deleteNote = (id, eventID) => call('DELETE', `/incidents/${id}/notes/${eventID}`);
+
+// alerts
+export const alerts = (query, opts) => call('GET', '/alerts', { query, ...opts });
+
+// schedule
+export const schedule = (from, to) => call('GET', '/schedule', { query: { from, to } });
+export async function onCallNow() {
+  try {
+    return await call('GET', '/schedule/current');
+  } catch (err) {
+    if (err instanceof ApiError && err.status === 404) return null;
+    throw err;
+  }
+}