docs(local-llms): add latency/cost comparison and deepseek-r1 transform pattern to evals doc
- Add Latency & Cost Comparison table: llama3.1:8b (~1m27s), qwen2.5-coder:32b
(~5-8m est.), deepseek-r1:32b (~5-8m est.) vs gemini-2.5-flash (~15-25s, $0.003)
and gpt-4o (~20-40s, $0.05-0.15) — all measured at 19 cases, concurrency=4
- Fix assertion pattern docs: single expressions required, not const/return blocks
- Add deepseek-r1 <think> strip transform pattern for promptfoo provider config
- Expand recommended models table with Disk, Reasoning, Pass Rate, and Notes columns