docs: add AMELIORATIONS.md with competitor feature analysis (#186)

Comprehensive analysis of missing features in cortex-cli compared to:
- Claude Code (Anthropic)
- Droid (Factory.ai)
- OpenCode (open-source)
- OpenAI Codex

Key findings include:
- Subagents/Multi-Agent orchestration (critical)
- Custom slash commands (critical)
- Plan mode (critical)
- Undo/redo commands (critical)
- Network proxy (critical from Codex)
- Chrome/browser integration (important)
- Question tool (important)
- Specification mode (important)

Document includes:
- Detailed feature descriptions with code examples
- Prioritization of improvements (Critical/Important/Useful)
- Complete comparison tables
- Implementation recommendations

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

Author: echobt