fix: don't backslash-escape quotes inside %"..."%" summary

Remind's %"..."%" delimiter treats the content literally, so a
backslash-escaped double quote shows up as a literal backslash in the
rendered message instead of being interpreted. Only escape quotes for
non-summary MSG bodies where the delimiter isn't %"..."%".

bin/remind.ml

@@ -257,13 +257,13 @@ let add_through b = function
 (** Escape special characters in the body of a MSG clause.
     - '%' must become '%%' (literal percent)
     - '[' must become '["["]' (a Remind expression that evaluates to the literal string "[") *)
-let escape_msg s =
+let escape_msg ?(summary = false) s =
   let buf = Buffer.create (String.length s) in
   String.iter
     (function
       | '\n' -> Buffer.add_string buf "\\n"
       | '\t' -> ()
-      | '"' -> Buffer.add_string buf "\\\""
+      | '"' -> if summary then Buffer.add_string buf "\"" else Buffer.add_string buf "\\\""
       | '%' -> Buffer.add_string buf "%%"
       | '[' -> Buffer.add_string buf {|["["]|}
       | c -> Buffer.add_char buf c)
@@ -272,7 +272,7 @@ let escape_msg s =
 
 let add_msg b ?(alarm = empty_alarm) ?(timed = false) summary =
   let has_alarm = alarm.day_delta <> "" || alarm.time_delta <> "" || alarm.sched <> "" in
-  let body = escape_msg summary in
+  let body = escape_msg summary ~summary:true in
   let body =
     if has_alarm then if timed then spf "%%\"%s%%\" (%%b %%3)" body else spf "%%\"%s%%\" (%%b)" body else body
   in