feat(tools): add Discord thread and channel management tool

[insecurejezza]

Summary

• add a Discord management tool for creating threads and text channels
• index active threads in the channel directory for downstream routing and discovery
• cover the new tool and directory behavior with regression tests

Test Plan

• source .venv/bin/activate
• python -m pytest -q tests/tools/test_discord_tool.py tests/gateway/test_channel_directory.py

[teknium1]

we need a way to work with this without tool use