feat(langchain): expose hak_tool_name in LangChain stream event metadata

#353 (predicates epic) must be fully complete before starting this task. #354 (monorepo migration) must also be complete — this change lives in the `hedera-agent-kit-langchain` adapter package.

JS reference: [PR #977](https://github.com/hashgraph/hedera-agent-kit-js/pull/977)

## Scope

- Inject `hak_tool_name` into `run_manager` metadata on tool invocation in the LangChain adapter
- No per-tool changes required — single injection point in the adapter wrapper

First confirm that #353 and #354 are complete, then inspect the hedera-agent-kit-langchain adapter package and its tool wrapper. Use the JS reference in PR #977 to understand the intended metadata behavior. Done means tool invocation adds hak_tool_name to run_manager metadata without requiring per-tool changes.

Written by the indexing model from the issue text.