✨ feat: add artifact-centered team collaboration

[pftg]

Summary

• make Team valuable for named coworker registration, immutable artifact handoffs, atomic call budgets, thread/fiber fan-out, normalized failures, revision lineage, and inspectable traces
• add a thin Team#run API while keeping routing, review loops, validation, and escalation in ordinary application Ruby
• simplify the blog workflow around Team artifacts: current You.com MCP-backed research, a deliberately weak writer, GPT editors, bounded feedback, senior-writer escalation, and final Ruby API validation
• keep the simple offline team example as cross-domain proof of the same Run and artifact primitives
• replace copied workflow coverage with behavioral VCR tests that prove a bad draft receives exact feedback, is reworked, escalates after bounded failure, and is reviewed again
• add a Tribunal eval beside the blog and preserve the live post and collaboration trace
• supersede generic refine and repair with a concise ADR and v5 roadmap requiring a second non-writing workflow before further lifecycle extraction

Product boundary

Team owns reusable collaboration state and safety. RubyLLM owns models, tools, provider retries, timeouts, and instrumentation. Application Ruby owns workflow order, quality policy, validators, escalation, persistence, and approvals. MCP and You.com remain example integrations, not core gem dependencies.

Verification

• bundle exec rake spec — 49 examples, 0 failures
• bundle exec rubocop — 20 files, no offenses
• gem build ruby_llm-team.gemspec — success; generated package removed afterward
• strict OKF validation — conformant, no issues
• live OpenRouter workflow — completed research, weak-writer revisions, senior escalation, fact re-audit, publication review, and Ruby validation
• bundle exec rake eval:blog — deterministic, relevance, faithfulness, and hallucination gates all pass
• VCR cassette contains only the three current hosted-review interactions

Review entry points

• README.md — why Team earns a Gemfile line and how the examples use it
• examples/blog/workflow.rb — explicit policy over Team artifacts
• examples/blog/research.rb — shared MCP-backed search and extraction tool
• examples/blog/trace.md — exact live collaboration and escalation path
• docs/decisions/2026-08-28-keep-quality-loops-in-application-ruby.md — current product decision
• docs/roadmaps/ROADMAP-v5.md — next cross-domain evidence plan