refactor(research): rewrite auto research module as Go event-driven pipeline

[crrow]

Context

The current Rust rara-research module has a monolithic run_iteration() that tightly couples all 14 pipeline steps. This makes it impossible to:

• Process multiple strategies concurrently
• Resume after process restart
• Decouple LLM generation/review from compilation/backtesting

Additionally, Rust toolchain is disk-heavy for the current hardware constraints.

Solution

Rewrite as a Go event-driven pipeline with:

• Persistent event queue (SQLite) — survives restarts, pending events resume
• Decoupled stages: Generate → Compile → Backtest → Review, each as independent event handler
• Strategy knowledge base (SQLite) — stores all hypotheses, backtest data, LLM reviews for historical context
• Feedback loop — rejected strategies trigger re-generation with historical context
• Auto-promotion — approved strategies PR to rara-strategies repo

Sprint Plan

Sprint 1: Foundation

• Go project scaffold, SQLite store, event queue, dispatcher, stage interface, CLI skeleton

Sprint 2: Pipeline Stages

• Generate, compile, backtest, review stages with LLM CLI executor integration

Sprint 3: Promotion + Polish

• Auto-PR to rara-strategies, feedback loop, status/history CLI, retry hardening

Acceptance Criteria

• Pipeline processes strategies end-to-end (generate → compile → backtest → review)
• Events persist in SQLite, resume after restart
• Approved strategies auto-PR to rara-strategies
• Rejected strategies re-enter pipeline with feedback context
• rara-research status and rara-research history CLI commands work