refactor(chat): decompose into modular architecture, add GM commands, fix protocol

- Extract ChatPanel monolith into 15+ focused modules under ui/chat/
  (ChatInput, ChatTabManager, ChatTabCompleter, ChatMarkupParser,
  ChatMarkupRenderer, ChatCommandRegistry, ChatBubbleManager,
  ChatSettings, MacroEvaluator, GameStateAdapter, InputModifierAdapter)
- Split 2700-line chat_panel_commands.cpp into 11 command modules
- Add GM command handling: 190-command data table, dot-prefix interception,
  tab-completion, /gmhelp with category filter
- Fix ChatType enum to match WoW wire protocol (SAY=0x01 not 0x00);
  values 0x00-0x1B shared across Vanilla/TBC/WotLK
- Fix BG_SYSTEM_* values from 82-84 (UB in bitmask shifts) to 0x24-0x26
- Fix infinite Enter key loop after teleport (disable TOGGLE_CHAT repeat,
  add 2-frame input cooldown)
- Add tests: chat_markup_parser, chat_tab_completer, gm_commands,
  macro_evaluator

Signed-off-by: Pavel Okhlopkov <pavel.okhlopkov@flant.com>

include/ui/chat/chat_utils.hpp

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "game/world_packets.hpp"
+#include <algorithm>
+#include <cctype>
+#include <string>
+
+namespace wowee {
+
+// Forward declaration
+namespace game { class GameHandler; }
+
+namespace ui {
+namespace chat_utils {
+
+/** Create a system-type chat message (used 15+ times throughout commands). */
+inline game::MessageChatData makeSystemMessage(const std::string& text) {
+    game::MessageChatData msg;
+    msg.type     = game::ChatType::SYSTEM;
+    msg.language = game::ChatLanguage::UNIVERSAL;
+    msg.message  = text;
+    return msg;
+}
+
+/** Trim leading/trailing whitespace from a string. */
+inline std::string trim(const std::string& s) {
+    size_t first = s.find_first_not_of(" \t\r\n");
+    if (first == std::string::npos) return "";
+    size_t last = s.find_last_not_of(" \t\r\n");
+    return s.substr(first, last - first + 1);
+}
+
+/** Convert string to lowercase (returns copy). */
+inline std::string toLower(std::string s) {
+    std::transform(s.begin(), s.end(), s.begin(), [](unsigned char c) {
+        return static_cast<char>(std::tolower(c));
+    });
+    return s;
+}
+
+} // namespace chat_utils
+} // namespace ui
+} // namespace wowee