docs(cortex-gui): comprehensive Zed & VSCode feature comparison roadmap (#329)

Add detailed analysis comparing Cortex GUI with Zed (216 crates) and VSCode
(91 contrib modules), identifying 15 high-priority features:

TIER 1 - Performance Critical (P0):
1. Rope data structure for large files (Zed: 2247 LOC)
2. Enhanced VirtualList with view pooling/recycling
3. Sum tree for O(log n) position calculations

TIER 2 - AI & Intelligence (P1):
4. Advanced Edit Predictions (Zed has 33K+ LOC)
5. True Multi-Buffer editing (Zed killer feature)
6. Async LSP with streaming & cancellation

TIER 3 - Visual & UX (P2):
7. GPU-accelerated minimap & rendering
8. Real-time CRDT collaboration
9. Incremental syntax highlighting (Tree-sitter)
10. Test Explorer with inline coverage

TIER 4 - Workflow & Integration (P3):
11. Enhanced Problem Matchers
12. Enhanced Sticky Scroll
13. Visual Keybinding Editor
14. Built-in Performance Profiler
15. Complete Workspace Trust Integration

Includes implementation examples, code snippets, estimated timelines,
and a phased implementation plan (19 weeks total).

Key insights:
- Zed: 216 Rust crates, 300K+ LOC, GPU rendering, Rope/SumTree
- VSCode: 91 contrib modules, 151K+ LOC, streaming LSP, RowCache
- Cortex GUI: 436 components, needs performance data structures

Co-authored-by: Droid Agent <droid@factory.ai>

Author: echobt