feat: add a traffic flow tool

Add get_traffic_flow over the traffic source's TomTom flow tiles. It
reports average speed as a share of free-flow speed, congested and
closed road length, and a breakdown by road category, stepping down a
zoom level when an area needs more tiles than the source reads at once.

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 - Add tools for language-model clients and a local MCP server. `npm run mcp`
   serves earthquake, active-fire, launch, aircraft, ship, satellite, camera, radio,
-  place, routing, bike-share, transit, weather, cyclone, fire-perimeter,
+  place, routing, bike-share, transit, traffic, weather, cyclone, fire-perimeter,
   terrain, installation and map-feature queries, plus a situation brief, over
   stdio to clients such as Claude Code, reading
   from a running app. Tools are defined