feat: add list_tools() method to HederaAgentAPI

#353 (predicates epic) must be fully complete before starting this task. T3 (#357) must also be complete — `list_tools()` exposes the `tool_type` field introduced there.

JS reference: [PR #992](https://github.com/hashgraph/hedera-agent-kit-js/pull/992)

## Scope

- Add `list_tools() -> list[ToolSummary]` method to `HederaAgentAPI`
- `ToolSummary` dataclass: `method: str`, `name: str`, `description: str`, `tool_type: ToolType`
- Export `ToolSummary` from the core package public API
- Covers all registered tools including plugins

First review the HederaAgentAPI entry point, the ToolType used by T3, and the core package public API; use JS PR #992 as a behavioral reference. Confirm prerequisites #353 and #357 are complete, then verify that list_tools() returns ToolSummary records for every registered tool and that ToolSummary is publicly exported.

Written by the indexing model from the issue text.