feat(rlm): Implement RLM Core Traits (LlmBackend, RlmEnvironment)

[ruvnet]

Summary

Implement the foundational traits for Recursive Language Model (RLM) integration as specified in ADR-014.

Tasks

• Define LlmBackend trait with generate, embed, and model info methods
• Define RlmEnvironment trait with retrieve, decompose, synthesize, answer_query methods
• Implement RuvLtraBackend using existing RuvLTRA model
• Add token budget tracking
• Add KV cache integration

References

• ADR-014: docs/adr/ADR-014-recursive-language-model-integration.md
• DDD-001: docs/ddd/DDD-001-recursive-language-model.md