[js] 0.20.0

feat: make qwen3.6-plus-free the default model, add compaction models cascade (#232)

• Change default model from minimax-m2.5-free to qwen3.6-plus-free (~1M context)
• Add --compaction-models CLI option for cascading compaction models
• Default cascade: (big-pickle nemotron-3-super-free minimax-m2.5-free gpt-5-nano qwen3.6-plus-free same)
• Add nemotron-3-super-free and qwen3.6-plus-free to free models lists
• Update documentation and provider priority lists

Related Pull Request: #234

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