Add v9.0 design analysis and recommendations

Comprehensive analysis of command_it v9.0 features based on real-world
production app usage (164 commands analyzed).

Three documents:
- COMMAND_PATTERNS_KNOWLEDGE_BASE.md: Generic patterns (error handling,
  undoable commands, chaining, best practices)
- V9_FEATURE_ANALYSIS_WATCHCRUNCH.md: Initial feature evaluation against
  real-world needs
- V9_FINAL_RECOMMENDATIONS.md: Validated recommendations after critical
  review (prioritizes standard filter library & CommandGroup)

Key findings:
- Standard error filter library has highest impact/effort ratio
- RetryableCommand has zero real-world demand (0/164 commands)
- Pattern-based hooks solve wrong granularity (cross-cutting vs command-specific)
- Refocused v9.0 achieves 55% boilerplate reduction vs 18% as designed

Author: escamoteur