* fix(buzz): accept a single mention-free channel id
`_mention_free` iterated the configured value directly, so one unquoted
UUID became a set of its characters and a numeric or boolean scalar
raised TypeError while the channel was being constructed. Both shapes are
documented as valid for the sibling Discord connector.
Parse the key through a dedicated helper that follows the Discord
convention: a scalar is a single entry, list entries are kept verbatim,
and an unusable entry never matches so `require_mention` stays in force.
* fix(channels): share scalar-or-list channel ID parsing
* docs(channels): keep guidance within CI size budget
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>