fix(email): encode Cyrillic binaries with /utf8.

OTP truncates non-ASCII in <<"...">> to 8-bit bytes, garbling Russian
in mail and in-app notification copy.

test/unit/logic_email_tests.erl

@@ -91,9 +91,13 @@ test_deliver_error() ->
 test_template_fill() ->
   {Sub, Plain, Html} = logic_email_templates:render(verify, <<"https://x/verify?token=z">>),
   ?assert(binary:match(Sub, <<"CalenTIQ">>) =/= nomatch),
+  %% OTP truncates Cyrillic in <<"...">> without /utf8 — guard real UTF-8 text
+  ?assert(binary:match(Sub, <<"подтвердите"/utf8>>) =/= nomatch),
+  ?assert(binary:match(Plain, <<"Подтвердите"/utf8>>) =/= nomatch),
   ?assert(binary:match(Plain, <<"https://x/verify?token=z">>) =/= nomatch),
   ?assert(binary:match(Html, <<"{{">>) =:= nomatch),
-  ?assert(binary:match(Html, <<"https://x/verify?token=z">>) =/= nomatch).
+  ?assert(binary:match(Html, <<"https://x/verify?token=z">>) =/= nomatch),
+  ?assert(binary:match(Html, <<"Подтвердите"/utf8>>) =/= nomatch).
 
 test_reminder_deliver() ->
   Self = self(),