fix(oidc): a sign-in links to an account by email only when the address was not set by the account itself

An SSO login that matched no account by its subject took the account with the
same email address and linked the provider identity to it. That address proves
nothing when the account typed it in itself: anyone could sign up with, or
switch their profile to, a colleague's address and receive the colleague's
first SSO login. The provider switch branch (#2110) relinked a row on any email
match without even asking for email_verified, and also for another subject of
the same provider.

users.email_self_asserted remembers an address the account set itself: signup
(not the first account) and an email change in the profile settings set it, an
admin entering a new address clears it, and accounts the provider creates start
without it. Existing accounts keep linking, except those whose address moved
away from the registered one without an admin editing it. A login by email now
needs a verified address and an unmarked account, and is refused for another
subject of the same issuer, with email_link_blocked and a translated message on
the login screen. An email change in the profile settings writes a
user.email_change audit row.

Refs #2110

server/src/nest/auth/auth.controller.ts

@@ -196,6 +196,11 @@ export class AuthController {
   async updateSettings(@CurrentUser() user: User, @Body() body: SettingsUpdateDto, @Req() req: Request) {
     const result = await this.profile.updateSettings(user.id, body);
     await this.auditApiKeys(user.id, result.changedKeys ?? [], req);
+    // The address itself stays out of the row, like the key values above; the row
+    // is what tells an admin later that the account chose its current address.
+    if (result.emailChanged) {
+      await this.audit.writeAudit({ userId: user.id, action: 'user.email_change', ip: getClientIp(req) });
+    }
     return { success: result.success, user: result.user };
   }