docs(cortex-gui): enhanced feature roadmap with Zed & VSCode comparison (#335)

This document provides a deep analysis comparing cortex-gui against Zed (216 crates)
and VSCode (91+ contrib modules), identifying 15 high-priority features to implement:

## P0 Critical (Performance):
1. Rope data structure for large files (2,248 LOC reference from Zed)
2. VirtualList with view pooling/recycling (854 LOC from Zed, 130 LOC from VSCode)
3. Sum Tree for O(log n) position calculations (1,835 LOC from Zed)

## P1 High (AI & Intelligence):
4. Advanced edit predictions (14K+ LOC in Zed)
5. Streaming diff for AI responses
6. Audio denoising for voice input (DTLN network)

## P2 Medium (Visual & UX):
7. GPU-accelerated minimap (WebGL/WebGPU)
8. Real-time CRDT collaboration (using Yjs)
9. Async LSP with streaming & cancellation
10. Inline test results & coverage

## P3 Nice to Have:
11. Web search integration
12. Incremental syntax highlighting (Tree-sitter)
13. Enhanced sticky scroll
14. Built-in performance profiler
15. Visual keybinding editor

Key findings:
- Cortex GUI: 436 components (strong coverage)
- Missing critical: Rope, Sum Tree, View Pooling
- EditPredictions: 192 LOC vs Zed's 14K+ LOC
- Estimated timeline: 21.5 weeks for full implementation

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

Author: echobt