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/i_modifier_state.hpp

@@ -0,0 +1,21 @@
+// IModifierState — abstract interface for keyboard modifier queries.
+// Allows unit testing macro conditionals without real input system. Phase 4.1.
+#pragma once
+
+namespace wowee {
+namespace ui {
+
+/**
+ * Read-only view of keyboard modifier state for macro conditional evaluation.
+ */
+class IModifierState {
+public:
+    virtual ~IModifierState() = default;
+
+    virtual bool isShiftHeld() const = 0;
+    virtual bool isCtrlHeld() const = 0;
+    virtual bool isAltHeld() const = 0;
+};
+
+} // namespace ui
+} // namespace wowee