backup-reauth: the account password before a backup or an export

Agreed with the owner on 2026-10-13, taken up on 2026-10-16 ("Да"); the
mockup is 1888dce. Both secret downloads - the full backup on Server ›
Backup and a domain's export on its settings - ask for "Your account
password": reauth (handlers_backup.go) checks the signed-in user's own
password with bcrypt, as a password change does, under the same limiter
(auth.AllowPasswordChange: ten in fifteen minutes per user, shared with the
Account form). A wrong or missing one is 401 on the same page with "Your
account password is incorrect.", logged; nothing is sent. The import and
the selfpost-backup CLI are not asked.

Also, the owner's phone screenshot of 2026-10-16 ("кнопка выбора файла не
такая, как в макете. Это косяк?"): the import's file field was a bare
<input type="file"> drawn by the browser ("Browse…"), where the mockup has
Bulma's .file - "Choose a file…" and the name chosen. The template now
follows the mockup; panel.js writes the name into .file-name on change and
at load (testdata/filename_test.js, run by TestPanelJS). No other file
field exists.

Tests: TestSecretDownloadsAskForTheAccountPassword (missing, wrong, right,
the limiter), the export refusals of the settings page with the password,
cmd/panel's restore tests and e2e's backups with it, e2e's refusal of a
backup without and with a wrong password. go vet + go test (26 packages)
and make e2e on the test server for this tree.

Docs: security.md § Backup and domain export, guide § Full backup and
restore, help (word for word with the mockup); CHANGELOG [Unreleased];
roadmap row done.

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

internal/web/handlers/handlers_outbound_pages_test.go

@@ -189,12 +189,12 @@ func TestDomainSettingsRefusalsStayOnTheSettingsPage(t *testing.T) {
 	}
 	has(t, "report address refusal", body, `Choose how aggregate reports are addressed for this domain.`)
 
-	code, body = post(s.h.HandleExportDomain, "export", url.Values{"encrypt": {"1"}, "password": {"short"}, "password_confirm": {"short"}})
+	code, body = post(s.h.HandleExportDomain, "export", url.Values{"encrypt": {"1"}, "password": {"short"}, "password_confirm": {"short"}, "account_password": {"correct-password-here!"}})
 	if code != http.StatusBadRequest {
 		t.Fatalf("a short export password = %d", code)
 	}
 	has(t, "export refusal", body, `The encryption password must be at least 12 characters.`, `<h1 class="title is-3">Domain settings</h1>`)
-	code, body = post(s.h.HandleExportDomain, "export", url.Values{"encrypt": {"1"}, "password": {"long-enough-password"}, "password_confirm": {"another-one-entirely"}})
+	code, body = post(s.h.HandleExportDomain, "export", url.Values{"encrypt": {"1"}, "password": {"long-enough-password"}, "password_confirm": {"another-one-entirely"}, "account_password": {"correct-password-here!"}})
 	if code != http.StatusBadRequest {
 		t.Fatalf("export passwords that differ = %d", code)
 	}