feat: add "e2ee encrypted" info message to all e2ee chats (#7008)

this PR adds a info message "messages are end-to-end-encrypted" also for
chats created by eg. vcards. by the removal of lock icons, this is a
good place to hint for that in addition; this is also what eg. whatsapp
and others are doing

the wording itself is tweaked at
https://github.com/deltachat/deltachat-android/pull/3817 (and there is
also the rough idea to make the message a little more outstanding, by
some more dedicated colors)

~~did not test in practise, if this leads to double "e2ee info messages"
on secure join, tests look good, however.~~ EDIT: did lots of practise
tests meanwhile :)

most of the changes in this PR are about test ...

ftr, in another PR, after 2.0 reeases, there could probably quite some
code cleanup wrt set-protection, protection-disabled etc.

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/mimeparser.rs

@@ -181,10 +181,10 @@ pub enum SystemMessage {
     /// Chat ephemeral message timer is changed.
     EphemeralTimerChanged = 10,
 
-    /// "Messages are guaranteed to be end-to-end encrypted from now on."
+    /// "Messages are end-to-end encrypted."
     ChatProtectionEnabled = 11,
 
-    /// "%1$s sent a message from another device."
+    /// "%1$s sent a message from another device.", deprecated 2025-07
     ChatProtectionDisabled = 12,
 
     /// Message can't be sent because of `Invalid unencrypted mail to <>`
@@ -213,6 +213,9 @@ pub enum SystemMessage {
 
     /// This message contains a users iroh node address.
     IrohNodeAddr = 40,
+
+    /// "Messages are end-to-end encrypted."
+    ChatE2ee = 50,
 }
 
 const MIME_AC_SETUP_FILE: &str = "application/autocrypt-setup";