[Client] Tabbed room channels with unread states and collapsible chat (#7478)

* [Client] Add room channel selector with per-channel chat views

* [Client] Tabbed room channels with unread states, collapse, read-only, banners

Reworks the room chat channel display: channels move out of the combobox
into a tab bar below the message input showing every channel available
to the user.

- Each tab shows its unread message count and is tinted when it holds
  unreads or a mention; both colors are user-configurable chat settings
  (channelUnreadColor, channelMentionColor) with a settings-page section.
- Clicking the active tab collapses the chat: message view and input
  hide and the splitter section minimizes to the tab strip; expanding
  restores the previous splitter sizes. Viewing a channel clears its
  unread state.
- Channels the user may read but not write (per write_access_level)
  show with the message input disabled and a read-only placeholder;
  sends are guarded locally, the server still enforces.
- Channel banner_message strings render at the top of their channel
  view on join, like the room join message on Main.
- Replayed channel history no longer inflates unread counts; moderation
  redaction now applies across all channel views.

* Fixup: keep chat tab bar visible when chat is collapsed

QSplitter children are collapsible by default, so setSizes({1, 0})
hid the whole chat group box including the channel tab bar.
Mark the chat widget non-collapsible so collapsing clamps to its
minimum size (title + tab bar) instead.

* [Room] Explicitly initialize MAIN_CHANNEL per review

* [Room] Address channel tab review follow-ups

- gate @all mentions on moderator/admin sender to match ChatView,
  whole-word matching for own name and highlight words
- hide single-channel tab bar so old servers do not show a lone Main
  tab that collapses chat on misclick
- capture target ChatView in sendMessage so errors land in the
  channel the message was sent from
- share ignore/unregistered filtering between RoomSay and
  RoomChannelSay via isRoomMessageIgnored

* [Client] Fix tab_room.cpp formatting per clang-format-18

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
Co-authored-by: BruebachL <bruebachl@cockatrice.example>

cockatrice/src/interface/widgets/settings_page/messages_settings_page.h

@@ -27,6 +27,8 @@ private slots:
     void actRemove();
     void updateColor(const QString &value);
     void updateHighlightColor(const QString &value);
+    void updateChannelUnreadColor(const QString &value);
+    void updateChannelMentionColor(const QString &value);
     void updateTextColor(QT_STATE_CHANGED_T value);
     void updateTextHighlightColor(QT_STATE_CHANGED_T value);
 
@@ -49,18 +51,27 @@ private:
     QCheckBox useGameTimeCheckBox;
     QGroupBox *chatGroupBox;
     QGroupBox *highlightGroupBox;
+    QGroupBox *channelGroupBox;
     QGroupBox *messageGroupBox;
     QLineEdit *mentionColor;
     QLineEdit *highlightColor;
+    QLineEdit *channelUnreadColor;
+    QLineEdit *channelMentionColor;
     QLineEdit *customAlertString;
     QLabel hexLabel;
     QLabel hexHighlightLabel;
+    QLabel channelUnreadColorLabel;
+    QLabel channelMentionColorLabel;
+    QLabel hexChannelUnreadLabel;
+    QLabel hexChannelMentionLabel;
     QLabel customAlertStringLabel;
     QLabel explainMessagesLabel;
 
     void storeSettings();
     void updateMentionPreview();
     void updateHighlightPreview();
+    void updateChannelUnreadPreview();
+    void updateChannelMentionPreview();
 };
 
 #endif // COCKATRICE_MESSAGES_SETTINGS_PAGE_H