feat: Add /force-encryption command and update message handling

Implement /force-encryption command to configure forced encryption
settings with on|off and policy resend-to-confirm|block options.

The changes enhance user experience by clarifying encryption requirements
and providing actionable commands. Users can now press Enter again to
confirm unencrypted messages in resend-to-confirm mode.

src/ui/ui.h

@@ -351,6 +351,7 @@ void cons_theme_properties(void);
 void cons_theme_colours(void);
 void cons_show_tlscert(const TLSCertificate* cert);
 void cons_show_tlscert_summary(const TLSCertificate* cert);
+void cons_encryption_setting(void);
 
 void cons_alert(ProfWin* alert_origin_window);
 void cons_remove_alert(ProfWin* window);