Previously a message like `<@&1490963422786093149> help` would spawn a
thread literally named `<@&1490963422786093149> help`, exposing raw
Discord mention markers in the thread list. Only user mentions
(`<@id>`) were being stripped upstream — role mentions (`<@&id>`) and
channel mentions (`<#id>`) leaked through.
Fix: strip all three mention patterns in `_auto_create_thread` before
building the thread name. Collapse runs of whitespace left by the
removal. If the entire content was mention-only, fall back to 'Hermes'
instead of an empty title.
Fixes#6336.
Tests: two new regression guards in test_discord_slash_commands.py
covering mixed-mention content and mention-only content.
Teknium
3f3d8a7b24