Implement Dungeon Finder UI window with role/dungeon selection

- Add renderDungeonFinderWindow() with status display (not queued /
  role check / queued+wait time / proposal / in dungeon / finished)
- Role checkboxes (Tank/Healer/DPS) and dungeon combo (25 entries
  covering Vanilla, TBC, and WotLK including Random/Heroic)
- Accept/Decline buttons during Proposal state, Teleport button
  while InDungeon, Leave Queue button while Queued/RoleCheck
- Store lfgProposalId_ on GameHandler so UI can pass it to
  lfgAcceptProposal(); expose getLfgProposalId() and
  getLfgTimeInQueueMs() getters
- Toggle window with I key (when chat input is not active)

include/ui/game_screen.hpp

@@ -227,6 +227,7 @@ private:
     void renderBankWindow(game::GameHandler& gameHandler);
     void renderGuildBankWindow(game::GameHandler& gameHandler);
     void renderAuctionHouseWindow(game::GameHandler& gameHandler);
+    void renderDungeonFinderWindow(game::GameHandler& gameHandler);
 
     /**
      * Inventory screen
@@ -259,6 +260,11 @@ private:
     int bagBarPickedSlot_ = -1;   // Visual drag in progress (-1 = none)
     int bagBarDragSource_ = -1;   // Mouse pressed on this slot, waiting for drag or click (-1 = none)
 
+    // Dungeon Finder state
+    bool  showDungeonFinder_ = false;
+    uint8_t lfgRoles_ = 0x08;  // default: DPS (0x02=tank, 0x04=healer, 0x08=dps)
+    uint32_t lfgSelectedDungeon_ = 861;  // default: random dungeon (entry 861 = Random Dungeon WotLK)
+
     // Chat settings
     bool chatShowTimestamps_ = false;
     int chatFontSize_ = 1;  // 0=small, 1=medium, 2=large