Dashboard: show the APRS numbers for all sources or for each source #454

The dashboard's APRS numbers are for the whole feed. With several sources, say a USB TNC-X, Dire Wolf and APRS-IS, there's no way to see what each one contributes. For example: stations heard by the TNC-X against stations heard by Dire Wolf (maintainer request, 2026-10-27).

Wanted

• A source picker on the dashboard: All sources (today's overview) or one source from the profile. Every APRS tile and sparkline then shows that source's numbers:
  • stations heard and new stations;
  • packets and packets a minute;
  • packet kinds, problems, the busiest stations and relays;
  • heard on RF, and the farthest direct hops.
• A comparison of the sources side by side: stations heard, packets, and the stations only that source heard. That answers "which TNC hears more, and what does each hear that the others miss?"
• It combines with the view filter (behavior 7) as today.
• The choice is kept per profile, like the range.

Counting per source

• Duplicates: a packet that two sources both bring counts for each source. Today the second copy is only noted as RecordSource (F1.25 behavior 9) and isn't counted again. The All sources view keeps counting it once.
• Storage: today only PacketsBySource and Sources (last packet time) are kept per source. The other counters need a source key in DashboardCounters' buckets, including the persisted history (Dashboard and GPS history kept across restarts #386).
• A source removed from the profile: its history stays until it ages out of the 24-hour range, labelled with its last name.

Notes

• Contract: Dashboard gains a per-source breakdown, or GetDashboardAsync takes an optional source id. A comparison needs the first.
• Stations heard per source on RF could come from APRS.NET's HeardStations (AprsNet.IGate, docs: plan 0.5.0–0.7.0, with features and gaps linked to their issues #213), recorded per source, if that fits better than new counters.