fix(web): add missing common.next/previous pagination keys

The bot session monitor paging controls use `common.next` and
`common.previous`, but those keys never existed in any locale. They were
only rendered because of the hardcoded `defaultValue: 'Next'`/`'Previous'`.
Removing those fallbacks (previous commit) made i18next render the raw key
name, so the Playwright smoke tests could no longer find the "Next" button.

Add `common.previous` and `common.next` to all 8 locales (reusing each
language's existing `guidedTour.previous`/`next` wording) and re-align the
locale key order with the `en-US` reference.

Verified locally:
- scripts/check-i18n.mjs passes for all locales
- every t('...') key referenced by BotSessionMonitor.tsx now exists in en-US
- tests/e2e/bot-session-tool-timeline.spec.ts: 13/13 passed (including the
  two request-recovery cases that failed in CI)
- prettier / tsc / eslint clean

web/src/i18n/locales/en-US.ts

@@ -307,6 +307,8 @@ const enUS = {
     customValue: 'Custom',
     loadFailed: 'Failed to load. Please try again.',
     search: 'Search',
+    previous: 'Previous',
+    next: 'Next',
     login: 'Login',
     logout: 'Logout',
     accountOptions: 'Settings',

web/src/i18n/locales/es-ES.ts

@@ -307,6 +307,8 @@ const esES = {
     customValue: 'Personalizado',
     loadFailed: 'No se pudo cargar. Inténtalo de nuevo.',
     search: 'Buscar',
+    previous: 'Anterior',
+    next: 'Siguiente',
     login: 'Iniciar sesión',
     logout: 'Cerrar sesión',
     accountOptions: 'Configuración',

web/src/i18n/locales/ja-JP.ts

@@ -303,6 +303,8 @@ const jaJP = {
     customValue: 'カスタム',
     loadFailed: '読み込みに失敗しました。再試行してください。',
     search: '検索',
+    previous: '前へ',
+    next: '次へ',
     login: 'ログイン',
     logout: 'ログアウト',
     accountOptions: 'システム設定',

web/src/i18n/locales/ru-RU.ts

@@ -306,6 +306,8 @@ const ruRU = {
     customValue: 'Свой вариант',
     loadFailed: 'Не удалось загрузить. Попробуйте ещё раз.',
     search: 'Поиск',
+    previous: 'Назад',
+    next: 'Далее',
     login: 'Войти',
     logout: 'Выйти',
     accountOptions: 'Настройки',

web/src/i18n/locales/th-TH.ts

@@ -301,6 +301,8 @@ const thTH = {
     customValue: 'กำหนดเอง',
     loadFailed: 'โหลดไม่สำเร็จ โปรดลองอีกครั้ง',
     search: 'ค้นหา',
+    previous: 'ขั้นตอนก่อนหน้า',
+    next: 'ถัดไป',
     login: 'เข้าสู่ระบบ',
     logout: 'ออกจากระบบ',
     accountOptions: 'การตั้งค่า',

web/src/i18n/locales/vi-VN.ts

@@ -304,6 +304,8 @@ const viVN = {
     customValue: 'Tùy chỉnh',
     loadFailed: 'Không tải được. Vui lòng thử lại.',
     search: 'Tìm kiếm',
+    previous: 'Bước trước',
+    next: 'Tiếp theo',
     login: 'Đăng nhập',
     logout: 'Đăng xuất',
     accountOptions: 'Cài đặt',

web/src/i18n/locales/zh-Hans.ts

@@ -287,6 +287,8 @@ const zhHans = {
     customValue: '自定义',
     loadFailed: '加载失败，请重试。',
     search: '搜索',
+    previous: '上一步',
+    next: '下一步',
     login: '登录',
     logout: '退出登录',
     accountOptions: '系统设置',

web/src/i18n/locales/zh-Hant.ts

@@ -283,6 +283,8 @@ const zhHant = {
     customValue: '自訂',
     loadFailed: '載入失敗，請重試。',
     search: '搜尋',
+    previous: '上一步',
+    next: '下一步',
     login: '登入',
     logout: '登出',
     accountOptions: '系統設定',