* MM-68845: Tighten authorization on /share-channel autocomplete
Require manage_shared_channels for the /share-channel slash command's
dynamic autocomplete suggestions, matching the equivalent gate already
enforced by /secure-connection autocomplete and by /share-channel
command execution.
* Clean up test comments and naming on /share-channel autocomplete tests
Drop verbose test docstrings, rename helpers and subtests to neutral
behavior-contract phrasing.
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Co-authored-by: Hanzo Dev <[email protected]>