fix(discord): reuse existing auto-thread on create race

[jeeves-assistant]

Summary

• Reuse an existing Discord starter-message thread when message.create_thread() loses a race to another bot/client.
• Avoid posting the fallback “Thread created by Hermes” seed message when the original message already has a thread.
• Add regression coverage for both message.thread and starter-message-id lookup paths.
• Refresh the branch against current main with a normal merge commit and add the release attribution mapping for this PR author.

Verification

• python3 -m py_compile scripts/release.py
• PYTHONPATH="$PWD" ~/.hermes/hermes-agent/venv/bin/python -m py_compile plugins/platforms/discord/adapter.py tests/gateway/test_discord_channel_controls.py tests/gateway/test_discord_slash_commands.py scripts/release.py
• env -u DISCORD_ALLOWED_CHANNELS -u DISCORD_REQUIRE_MENTION -u DISCORD_FREE_RESPONSE_CHANNELS -u DISCORD_IGNORED_CHANNELS -u DISCORD_NO_THREAD_CHANNELS PYTHONPATH="$PWD" ~/.hermes/hermes-agent/venv/bin/python -m pytest tests/gateway/test_discord_channel_controls.py tests/gateway/test_discord_slash_commands.py -q -k 'auto_create_thread or auto_thread' -o 'addopts='
• git diff --check

Notes

This fixes the duplicate-thread class seen when multiple Discord bots share a channel and one creates a thread from the user’s starter message before another adapter handles the same message.

PR #48690 covered the same race and is being closed as the duplicate; this PR remains the artifact of record.

[jeeves-assistant]

Closing this stale agent-authored PR per the approved cleanup matrix. Evidence: it is currently conflicted/dirty and touches bundled Hermes Discord adapter/release-attribution code. The duplicate-thread bug may still be valid, but resolving this PR would require forbidden core/plugin conflict work in this lane.