Move GuiEventHandlerBase to Abstractions (renderer-agnostic)

Extract all event routing, text input management, signal subscriptions,
and TextInputState callback wiring to GuiEventHandlerBase in Abstractions.
The class works with IGuiChrome interface instead of VkGuiRenderer directly.

- IGuiChrome: interface for ActiveTab, EquipmentState, PlannerChartRect, Bus
- VkGuiRenderer implements IGuiChrome
- GuiEventHandlers in Gui is a 20-line wrapper

Total code moved from Gui to Abstractions this session:
  Tabs: 2,133 lines, EventHandler: 600 lines, States: ~100 lines
  Gui wrappers: 11+11+11+20 = 53 lines

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sebgod