Code Quality: Complete dock.gd decomposition by extracting File I/O, Visgroups, and Signal Wiring

[saworbit]

Context

While the tab handler split extracted the 4 tab controllers (\dock_brush_handler.gd, \dock_paint_handler.gd, \dock_entity_handler.gd, \dock_manage_handler.gd), \dock.gd\ remains ~6,000 lines long.

Remaining Responsibilities in \dock.gd\

• File I/O & Export Dialogs: .hflevel, .map\ import/export, .glb\ export, and autosave dialog workflows.
• Visgroup Operations: Visgroup creation, deletion, visibility toggles, and membership sync.
• Cordon Controls & UV Alignment: Cordon bounds editing, UV reproject/justify signal handlers.
• Signal Wiring: Over 100 signal connections between dock UI controls, LevelRoot signals, and subsystem events.
• Schema Builders: Shared property dispatch between entity properties and external tool settings.

Proposed Solution

1. Extract file I/O and dialog management into \dock_file_handler.gd.
2. Extract visgroup management into \dock_visgroup_handler.gd.
3. Move signal connections setup into \dock_connections.gd.
4. Target a minimal, readable \dock.gd\ orchestrator (~1,200–1,500 lines).

[saworbit]

Fixed in PR #72. File operations, visgroup and cordon workflows, and dock signal wiring now live in focused modules with thin dock callbacks. The full GUT suite and pull request checks pass.