The `getPluginCommandSpecs` gate only checked `nativeCommandsAutoEnabled`,
which Slack sets to `false`. This caused plugin-registered slash commands
(e.g. /lcm, /lossless from lossless-claw) to be silently excluded from
Slack, even though Slack declares `capabilities.nativeCommands: true` and
the user explicitly enables native commands via config.
The fix widens the gate to also pass when the channel plugin declares
`capabilities.nativeCommands === true`, and adds the
`getPluginCommandSpecs` integration to the Slack slash command setup so
plugin commands are merged into the native command list.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
