Provide integration adapters (LangChain/LlamaIndex) (v1.x)

## Problem
Common frameworks need adapters to enforce local transformation before model calls.

## Scope
- Wrapper modules for at least one framework.
- Minimal configuration; secure defaults.

## Acceptance Criteria
- At least one adapter documented.
- Example integration in docs.

## Notes
Adapters should preserve v0.x guarantees.