feat(web): sign-in, first-run setup, app shell and user admin (M1)

- core: AuthSession keeps the access token in memory, refreshes it
  once for all parallel requests (single-flight) and retries them;
  refresh races between tabs are retried, reuse signs out; ApiError
  carries problem+json codes and field errors
- web: TanStack Router with guards — guests go to /login, the bootstrap
  admin to /setup/admin, temporary passwords to /setup/password, admin
  pages by role
- login, setup screens, Classic shell (top bar, role-based sidebar,
  empty player), settings: name, theme, language, password, devices
- users admin: search, role filter, create with a one-time temporary
  password, reset, block, role change, delete as the policy allows;
  audit log for admins
- ru/en strings for auth, admin and error codes; language and theme
  are saved in the profile

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/pages/SetupPage.tsx

@@ -0,0 +1,108 @@
+import { unwrap } from '@pipu/core';
+import { useState, type FormEvent } from 'react';
+import { useTranslation } from 'react-i18next';
+
+import { useAuthState, useSession, useUser } from '../app/session';
+import { useErrorText, useFieldError } from '../shared/lib/errors';
+import { lockResetIcon, shieldIcon } from '../shared/ui/icons';
+import { Button, Field, FormError, Icon } from '../shared/ui/ui';
+import { AuthLayout } from './AuthLayout';
+import s from './auth.module.css';
+
+/** Обязательный шаг после входа: новые логин и пароль админа (admin) или замена временного пароля (password). */
+export function SetupPage({ variant }: { variant: 'admin' | 'password' }) {
+  return useAuthState().status === 'signed_in' ? <SetupForm variant={variant} /> : null;
+}
+
+function SetupForm({ variant }: { variant: 'admin' | 'password' }) {
+  const { t } = useTranslation(['auth', 'common']);
+  const session = useSession();
+  const user = useUser();
+  const errorText = useErrorText();
+  const fieldError = useFieldError();
+  const admin = variant === 'admin';
+  const minLength = user.role === 'user' ? 8 : 12;
+
+  const [username, setUsername] = useState(user.username);
+  const [password, setPassword] = useState('');
+  const [repeat, setRepeat] = useState('');
+  const [busy, setBusy] = useState(false);
+  const [error, setError] = useState<unknown>(null);
+  const mismatch = repeat !== '' && repeat !== password;
+
+  const submit = async (e: FormEvent) => {
+    e.preventDefault();
+    if (mismatch) return;
+    setBusy(true);
+    setError(null);
+    try {
+      const res = admin
+        ? await session.client.POST('/api/v1/me/bootstrap-credentials', {
+            body: { new_username: username.trim(), new_password: password },
+          })
+        : await session.client.POST('/api/v1/me/password', { body: { new_password: password } });
+      await session.apply(unwrap(res));
+    } catch (err) {
+      setError(err);
+      setBusy(false);
+    }
+  };
+
+  const usernameError = fieldError(error, 'new_username');
+  const passwordError = fieldError(error, 'new_password');
+  const generalError = error && !usernameError && !passwordError ? errorText(error) : null;
+
+  return (
+    <AuthLayout>
+      <span className={s.badge}>
+        <Icon src={admin ? shieldIcon : lockResetIcon} size={16} />
+        {t(admin ? 'setup.admin_badge' : 'setup.password_badge')}
+      </span>
+      <h1>{t(admin ? 'setup.admin_title' : 'setup.password_title')}</h1>
+      <p className={s.lead}>{t(admin ? 'setup.admin_text' : 'setup.password_text')}</p>
+      <form onSubmit={(e) => void submit(e)} noValidate>
+        {admin && (
+          <Field
+            label={t('setup.new_username')}
+            value={username}
+            onChange={setUsername}
+            autoComplete="username"
+            autoCapitalize="none"
+            spellCheck={false}
+            error={usernameError}
+          />
+        )}
+        <Field
+          label={t('setup.new_password')}
+          type="password"
+          value={password}
+          onChange={setPassword}
+          autoComplete="new-password"
+          hint={t('setup.min_length', { min: minLength })}
+          error={passwordError}
+        />
+        <Field
+          label={t('setup.repeat_password')}
+          type="password"
+          value={repeat}
+          onChange={setRepeat}
+          autoComplete="new-password"
+          error={mismatch ? t('common:form.passwords_mismatch') : undefined}
+        />
+        <FormError>{generalError}</FormError>
+        <Button
+          type="submit"
+          variant="primary"
+          className={s.submit}
+          busy={busy}
+          disabled={!password || password !== repeat || (admin && !username.trim())}
+        >
+          {t('setup.submit')}
+        </Button>
+        <Button variant="ghost" className={s.link} onClick={() => void session.logout()}>
+          {t('setup.logout')}
+        </Button>
+      </form>
+    </AuthLayout>
+  );
+}