`GatewayInboundMixin._hm_pre_gateway_dispatch_hook` was a plain `def` calling
the sync `hermes_cli.lifecycle.invoke_hook` from the async `_hm_admit_event`,
so an `async def pre_gateway_dispatch` callback was resolved through
`resolve_plugin_command_result` on a helper thread with its own loop: the
gateway loop blocked for the callback's whole duration and any loop-bound await
(an `asyncio.Event` set by a loop task, a loop-bound aiohttp session,
`asyncio.to_thread`) could never complete, failing at 30s.
Add `PluginManager.ainvoke_hook` (+ `hermes_cli.plugins.ainvoke_hook` /
`hermes_cli.lifecycle.ainvoke_hook`): same payload narrowing (shared
`_hook_callback_kwargs`), observer + isolation semantics and result contract as
`invoke_hook`, but awaitable results are awaited on the caller's loop.
`pre_gateway_dispatch` stays intentionally unbounded. The inbound hook becomes
`async def` and `_hm_admit_event` awaits it; the sync `invoke_hook` is untouched
for every other caller. Existing tests that stubbed the hook synchronously are
adapted to the async seam.
Fixes#110241
Salvages #110265
(cherry picked from commit 22bb10d305c7992f43bbfdf1481ad0ef0015b2b7)
