feat(tools): count and summarize every match in the area tools

aircraft_in_area and vessels_in_area return at most 200 rows, so a client
asked which operators dominate an area, or the average altitude there, could
only estimate from a truncated sample. Both tools now take an optional
group_by (aircraft: operator, origin_country, type_code; ships: type,
destination) and stats (airborne altitude and speed for aircraft, speed for
ships). Each is computed over every match before rows are capped. Breakdowns
list the ten largest groups plus other and unknown counts, and the summary
names the three largest.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+- `aircraft_in_area` and `vessels_in_area` take `group_by` and `stats`, so a
+  client can ask which operators or ship types dominate an area, or the average
+  altitude or speed, over every match instead of estimating from the returned
+  rows.
+
 - Treat explicitly current, complete empty vessel coverage as a successful update,
   clearing obsolete contacts while retaining stale or incomplete snapshots.