feat: add reflexion plugin for self-refinement

[amondnet]

Summary

Add a reflexion plugin that implements self-refinement techniques based on academic research (Self-Refine, Reflexion papers). This plugin introduces feedback and refinement loops to improve output quality by 8-21%.

Background

Based on:

• Self-Refine - Iterative refinement
• Reflexion - Self-reflection for agents
• Agentic Context Engineering - Memory updates (10.6% improvement)

Reference implementation: ref/context-engineering-kit/plugins/reflexion/

Proposed Structure

plugins/reflexion/
├── .claude-plugin/
│   └── plugin.json
├── README.md
└── commands/
    ├── reflect.md      # Self-refinement with complexity triage
    ├── critique.md     # Multi-agent review (3 judges)
    └── memorize.md     # CLAUDE.md context curation

Tasks

• T001 [P] Create plugin directory structure
• T002 [P] Create plugin.json manifest
• T003 Create README.md with documentation
• T004 Create reflect.md command (depends on T001)
• T005 Create critique.md command (depends on T001)
• T006 Create memorize.md command (depends on T001)

Dependencies & Execution Order

Parallel Group 1 (independent):

• T001: Directory structure
• T002: Plugin manifest

Sequential:

1. T003: README (after T001)
2. T004-T006: Commands (after T001)

Acceptance Criteria

• Plugin follows context-engineering-kit pattern
• All 3 commands work correctly
• README documents usage and scientific foundation
• Plugin can be installed via Claude Code