bug(render-map-tool): single-target prompts (e.g. "show Eiffel Tower") render multiple pins

[mattpodwysocki]

Context

Feedback from @jussi-salminen during QA of #199. Reproducible in the "mapbox-default" video he attached.

Problem

For prompts that name a single specific place — "show the Eiffel Tower on a map" — render_map_tool renders multiple pins instead of one. This is confusing for the user: a single-target query should produce a single, unambiguous result.

Likely causes (need investigation)

• Upstream search (search_and_geocode_tool / category_search_tool) returns multiple features and the render tool passes them all to the iframe payload without deduping
• The render tool isn't filtering by relevance/confidence score
• The agent itself invokes render_map_tool with multiple coordinate refs and the tool faithfully draws all of them

Acceptance

• Reproduce against the "show Eiffel Tower on map" prompt
• Identify which layer (upstream search, render tool, or agent) is responsible
• Single-target prompts render exactly one pin
• Multi-target prompts ("show all coffee shops near…") still render the full set