feat: put offline, privacy and about on settings pages of their own and widen the settings search

Offline sat in the middle of Backup & reset, privacy settings were spread
over Reading, Composing and Message list, and the version card took room
from the page list in the sidebar's footer. The search matched letters
inside words ("lock" found Time format and Send Checks) and knew no other
words for a setting ("offline", "autoreply", "logout" found nothing).

- Offline is a page in the top group: Keep mail on this device, what is
  kept, Remove everything from this device, and the Outbox as its own
  section. Old `/settings/backup/offline` links and the offline notice
  land there.
- Privacy holds remote images and trusted senders, read receipts, sender
  pictures from the web, the desktop app's usage info and crash reports,
  and a link to the push relay on Notifications. Reading, Composing and
  Message list keep a link row; old links to those sections land on
  Privacy.
- About is the last page and holds the version card; the footer keeps the
  Advanced switch.
- The search matches whole words and word starts (substrings only in
  Chinese, Japanese and Thai), and each row can carry synonyms in the
  user's language. A page matches by its name and keywords or when one of
  its rows has every word. Account gets a Sign out row so "logout" leads
  somewhere.
- The index test now also fails when a page draws a section the index
  doesn't know, and a new test fails on two indexed rows with the same
  name. Tests that rendered remote content and sender pictures on Reading
  and Message list render Privacy instead, since that's where the rows are.

components/admin/org/sections/offline-section.tsx

@@ -55,7 +55,7 @@ export function OfflineSection({ draft }: { draft: OrgPolicyDraft }) {
     <SettingsSection
       id="offline"
       title="Offline mode"
-      description="People can keep mail on a device to read and write it without a connection. In browsers it is off until someone turns on “Keep mail on this device” in Settings > Backup & reset. In the Bulwark desktop app it is on unless you forbid it here."
+      description="People can keep mail on a device to read and write it without a connection. In browsers it is off until someone turns on “Keep mail on this device” in Settings > Offline. In the Bulwark desktop app it is on unless you forbid it here."
     >
       <SettingItem
         label="Don't let people keep mail on their devices"