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_command_registry.hpp

@@ -0,0 +1,50 @@
+// ChatCommandRegistry — command registration + dispatch.
+// Replaces the 500-line if/else chain in sendChatMessage() (Phase 3.1).
+#pragma once
+
+#include "ui/chat/i_chat_command.hpp"
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace wowee {
+namespace ui {
+
+/**
+ * Registry of all slash commands.
+ *
+ * dispatch() looks up the command by alias and calls execute().
+ * getCompletions() provides tab-completion for /command prefixes.
+ */
+class ChatCommandRegistry {
+public:
+    /** Register a command (takes ownership). All aliases are mapped. */
+    void registerCommand(std::unique_ptr<IChatCommand> cmd);
+
+    /**
+     * Dispatch a slash command.
+     * @param cmdLower  lowercase command name (e.g. "cast", "whisper")
+     * @param ctx       context with args, gameHandler, services, etc.
+     * @return result indicating if handled and whether to clear input
+     */
+    ChatCommandResult dispatch(const std::string& cmdLower, ChatCommandContext& ctx);
+
+    /** Get all command aliases matching a prefix (for tab completion). */
+    std::vector<std::string> getCompletions(const std::string& prefix) const;
+
+    /** Get help entries: (alias, helpText) for all registered commands. */
+    std::vector<std::pair<std::string, std::string>> getHelpEntries() const;
+
+    /** Check if a command alias is registered. */
+    bool hasCommand(const std::string& alias) const;
+
+private:
+    // alias → raw pointer (non-owning, commands_ owns the objects)
+    std::unordered_map<std::string, IChatCommand*> commandMap_;
+    // Ownership of all registered commands
+    std::vector<std::unique_ptr<IChatCommand>> commands_;
+};
+
+} // namespace ui
+} // namespace wowee