Fix text chat functionality

[urbanawakening]

What does this PR do?

Fixes the in-game chat system + reimplements the chat renderer.

Input layer:

• Adds Screen::injectKeyPressed() public wrapper so the Win64 WndProc can forward key events into the active screen's protected keyPressed() handler.
• Routes WM_CHAR (printable characters, Enter) and WM_KEYDOWN (Escape, Backspace, arrows, Tab) from WndProc to the active screen, returning 0 to consume handled events before they reach gameplay input (g_KBMInput).
• Adds KeyboardConstFromVK() helper to map Win32 virtual key codes back to Keyboard::KEY_* constants.
• Fixes the chat-open hotkey (T) to use edge detection (s_chatKeyWasDown) so it only fires on key-down, not while held.

Text editing:

• Adds caretPos member to ChatScreen with full caret-based editing: insert at position, backspace at caret, left/right arrow navigation, and blinking cursor in render.
• Fixes a static initialization order bug where ChatScreen::allowedChars was an empty copy of SharedConstants::acceptableLetters — now references the source string directly at runtime.

Networking:

• Re-enables PlayerConnection::handleChat (was #if 0): formats messages as <PlayerName> text and broadcasts via PlayerList::broadcastAll().
• Adds explicit case ChatPacket::e_ChatCustom in ClientConnection::handleChat to display incoming raw chat messages.

Rendering:

• Re-enables the OpenGL chat message renderer in Gui::render() (was #if 0), repositioned from overlapping the health bar to 40px above the toolbar.
• Disables the duplicate Iggy/flash chat labels in UIScene_HUD::handleTimerComplete() by zeroing all m_labelChatText opacities, consolidating chat display into the single Gui.cpp path.

Why?

The Win64 port had no working chat. Pressing T would basically softlock you.

How to test

• Launch a singleplayer world, press T, chat input bar appears at screen bottom with blinking cursor
• Type a message, verify characters appear and caret moves correctly
• Use Backspace to delete, Left/Right arrows to move cursor, then press Enter to send
• Verify the sent message appears in the chat history above the toolbar with dark gray background
• Press Escape while chat is open, chat closes, pause menu does NOT open
• Verify chat messages fade out after ~10 seconds when not actively chatting

Checklist

• Builds without errors
• Tested in-game
• No new warnings

[coah80]

i did not mean to click dat shit