Allow fixing an account's credentials from a failed test

An imported account with a wrong password could only be deleted and
re-added, which loses its folder mapping and its migration journal.
Clicking either FAIL badge now opens a dialog for both logins and both
passwords.

Passwords are never sent to the browser, so the password fields start
empty and an empty field keeps the stored ciphertext — one side can be
corrected without retyping the other. Saving resets both test verdicts
to unknown: they described the previous credentials, and the run gate
requires a passing test on both sides, so the account cannot start on an
unverified password.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/store/accounts.go

@@ -32,6 +32,21 @@ func (s *Store) CreateAccount(ctx context.Context, a Account) (int64, error) {
 	return id, err
 }
 
+// UpdateAccountCredentials replaces an account's logins and, when a new
+// ciphertext is supplied, its passwords; a nil password keeps the stored one so
+// the operator can fix only the side that failed. Both connection tests are
+// reset to "unknown" because the previous verdicts no longer describe these
+// credentials, which also forces a re-test before the account can run.
+func (s *Store) UpdateAccountCredentials(ctx context.Context, id int64, srcLogin, dstLogin string, srcPassEnc, dstPassEnc *string) error {
+	_, err := s.Pool.Exec(ctx,
+		`UPDATE accounts SET src_login=$2, dst_login=$3,
+		 src_pass_enc=COALESCE($4, src_pass_enc), dst_pass_enc=COALESCE($5, dst_pass_enc),
+		 test_src_status='unknown', test_dst_status='unknown', last_error=''
+		 WHERE id=$1`,
+		id, srcLogin, dstLogin, srcPassEnc, dstPassEnc)
+	return err
+}
+
 // DeleteAccount removes one account (and its migrated_messages via ON DELETE CASCADE).
 func (s *Store) DeleteAccount(ctx context.Context, id int64) error {
 	_, err := s.Pool.Exec(ctx, `DELETE FROM accounts WHERE id=$1`, id)