Mounts <FilterPanel> (from #274) on ReportsTrendsPage next to the period
selector, and threads accountIds from useReportsPeriod through useTrends
into getMonthlyTrends/getCategoryOverTime (both already accountIds-aware
since #273). The account checkbox list reuses the same getAllImportSources
query as the Transactions single-source filter. Empty selection = no
filter, byte-identical to pre-#275 output.
Resolves#275