`queryCalendarEvents` forwarded the `MutableStateFlow` it accumulates
the provider results in, so the initial empty value was the first thing
collectors saw - before any provider had reported. Callers in the
launcher take that first result (`CalendarPartProvider` uses `.first()`)
and cannot tell it apart from "no events", so the agenda stayed empty
and its part never showed up.
`CalendarRepository.findMany`'s 500 ms debounce used to hide this: the
placeholder was superseded by the real list within the debounce window,
which is exactly why the agenda only ever appeared half a second late.
Keep the accumulator null until the first provider reports, and let
`findMany` - a one-shot query for the clock and calendar widgets - wait
for all providers (`awaitAllProviders`) so it never hands out a partial
list. The search path keeps streaming results as providers report, now
without an empty flash.
`CalendarRepository.findMany` holds every result back by 500 ms, which
was added for the calendar widget to collapse bursts of plugin and
permission changes. `debounce` delays the first result too, so the
agenda part - whose ranking stays 0 until the first result arrives -
only appeared half a second after the clock and the other parts.
The agenda is re-queried on a calendar change or every 15 minutes, so
it does not need the debounce. Make the delay a parameter (still 500 ms
by default) and pass 0 from `CalendarPartProvider`.
