fix: unify transaction-tool hook invocation via BaseTransactionTool

#353 (predicates epic) must be fully complete before starting this task. #357 must also be complete — this task builds on `BaseTransactionTool`.

**Land alongside #361 (doc fix for issue #339).**

Hook invocation is currently duplicated per-tool. The JS repo centralized it in `BaseTransactionTool` so that all transaction tools get consistent pre/post-execution hook firing without per-tool wiring.

JS reference: [PR #1047](https://github.com/hashgraph/hedera-agent-kit-js/pull/1047)
Python tracking: [Issue #339](https://github.com/hashgraph/hedera-agent-kit-py/issues/339)

## Scope

- Move hook invocation into `BaseTransactionTool.execute()` so it fires uniformly for every transaction tool
- Remove per-tool hook wiring duplications across built-in plugins
- Regression test: a `RejectToolPolicy` targeting a known tool must fire correctly end-to-end

First confirm that #353 and #357 are complete, then read BaseTransactionTool.execute() and the built-in plugin transaction tools for duplicated hook wiring. Use the JS PR #1047 as context and exercise the RejectToolPolicy regression path. Done means hooks fire consistently through BaseTransactionTool without per-tool duplication, with the end-to-end rejection behavior covered.

Written by the indexing model from the issue text.