add: V4.2 Final Report — complete project retrospective with evidence-based analysis

Create v4_2-handoff.md

docs: add V4.1 run report — detailed evaluation with per-task analysis and V4.2 roadmap

Create v4_1-handoff.md

docs: add V4 run assessment with lessons learned and improvement roadmap

ADR-002: V4 Instruct-Only GRPO — revises dual-model plan based on model repo audit

Add comprehensive investigation report — performance audit, unexplored alternatives, literature-backed recommendations

Add session checkpoint: v3 launch decision with full context

Add v3 thinking control patch - task-aware system prompts + think efficiency reward

docs: add ADR-001 next steps with detailed execution plans

docs: add project documentation