Settings: tabs instead of one long page, and a review pass (#5916)

Settings was every registry group, then invites, accounts, groups and
activity, in one scroll. It is now six tabs held in ?tab=:
- General: General, Notes, Attachments, Links.
- People: Access, Invites, Accounts, Groups.
- Email, with a line saying whether email is on and what it still needs.
- Security.
- Activity.
A registry group that no tab names lands on General, so it can't go missing.

Save saves only the current tab. Edits waiting on other tabs keep their
values and mark their tab with a dot. Leaving the page with unsaved edits
asks first.

Review fixes:
- On a phone, a field stacks under its label instead of overflowing beside
  it.
- Descriptions are easier to read.
- The SMTP encryption choice shows readable names (choice_labels).
- The test-email button uses .btn-sm and is disabled while email is off.
- The accounts list is headed Accounts, not People, now that People is a
  tab.
- The docs point at the new paths.

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

docs/public-hosting.md

@@ -23,10 +23,10 @@ matters.
 **Instances that predate this still need one manual flip.** The close fires when the
 first account is created, so a server whose admin already existed keeps whatever
 `allow_registration` was set to — which was **on** by default. Check **Settings →
-Access → Allow new registrations** before exposing an instance you have been running
+People → Allow new registrations** before exposing an instance you have been running
 on a LAN.
 
-To let someone else in, send them an invite: **Settings → Invites** makes a link that
+To let someone else in, send them an invite: **Settings → People → Invites** makes a link that
 works once, expires (a week by default), and can be pinned to one email address. It
 lets that one person register while registration stays closed.
 
@@ -146,7 +146,7 @@ address can be sent.
 ## Storage per account
 
 Each account may store up to `storage_quota_gb` of attachments (Settings →
-Attachments, 5 GB by default; 0 means no limit). Admins have no limit. Trashed notes
+General → Attachments, 5 GB by default; 0 means no limit). Admins have no limit. Trashed notes
 count until the trash is emptied, because their files are still on disk. An upload
 past the limit is refused with 507 Insufficient Storage, and a phone or desktop
 retries that file on each sync, so it goes through once there is room. The Account