M5: Windows client moderation UI; add C ABI getters for account list, user mute/deafen, channel topic

core/src/session/session.h

@@ -22,6 +22,7 @@ struct Channel {
     uint32_t    id{0};
     uint32_t    parent_id{0};
     std::string name;
+    std::string topic;
     bool        password_protected{false};
     uint32_t    max_users{0};
 };
@@ -51,6 +52,8 @@ struct User {
     std::string         nickname;
     bool                is_guest{true};
     uint32_t            channel_id{0};
+    bool                self_mic_muted{false};
+    bool                self_deafened{false};
     bool                server_muted{false};
     bool                server_deafened{false};
     std::vector<Stream> streams;