chore(deps): move to kotlinx-datetime 0.8 and coroutines 1.11

[kaulith]

Picks up the bumps from #31, which cannot build as it stands: 0.5.0 to 0.8.0 crosses the 0.7.0 removals.

kotlinx.datetime.Instant and kotlinx.datetime.Clock no longer exist in 0.8.0. The 0.7.1 typealiases were dropped again before release, so 26 files move to kotlin.time.Instant and kotlin.time.Clock. Kotlin 2.4 has both stable, so no opt-in is needed.

dayOfMonth and monthNumber were renamed in 0.7.0, which touches six call sites. Month.number is a top-level extension, so ReportColumn and AnalyticsViewModel gain import kotlinx.datetime.number; ReportConfig takes the Month constructor overload instead. The two dayOfMonth uses in DateRangeSheet are java.time from the calendar library and stay.

Nothing else in 0.7.0 reaches this code: no kotlinx serialization, and the only TimeZone.UTC use is toInstant, not an identifier comparison. Room converters still persist epoch milliseconds, so the committed schemas are unchanged.