feat: add place search and routing tools

Add search_places and places_nearby over the app's Google Places routes,
and plan_route over its OpenStreetMap routing. The place search service
reports when no search key is configured, so an unconfigured server is
not mistaken for an empty result, and rate limits become retry_later.
Route endpoints accept a place name or coordinates.

src/tools/area.js

@@ -93,6 +93,53 @@ function circleArea(lat, lon, radiusKm) {
   };
 }
 
+/** JSON Schema for a single location: a place name, or lat and lon. */
+export const POINT_SCHEMA = Object.freeze({
+  type: 'object',
+  description: 'A place name, or lat and lon.',
+  properties: {
+    place: { type: 'string', minLength: 1, maxLength: 200 },
+    lat: { type: 'number', minimum: -90, maximum: 90 },
+    lon: { type: 'number', minimum: -180, maximum: 180 },
+  },
+  additionalProperties: false,
+});
+
+/** Resolve a point argument to `{ label, lat, lon }`. */
+export async function resolvePoint(point, { services, signal } = {}) {
+  if (point?.place != null && point.lat == null && point.lon == null) {
+    const area = await resolveArea(
+      { place: point.place },
+      { services, signal },
+    );
+    return { label: area.label, ...areaCenter(area) };
+  }
+  if (point?.place == null && point?.lat != null && point?.lon != null)
+    return {
+      label: `${point.lat.toFixed(4)}, ${point.lon.toFixed(4)}`,
+      lat: point.lat,
+      lon: point.lon,
+    };
+  throw new ToolError(
+    'invalid_arguments',
+    'A location needs either place, or lat and lon',
+  );
+}
+
+/** Distance in kilometers from an area's center to its farthest edge point. */
+export function areaRadiusKm(area) {
+  if (area.center) return area.center.radiusKm;
+  const center = areaCenter(area);
+  return Math.max(
+    ...[
+      { lat: area.north, lon: area.west },
+      { lat: area.north, lon: area.east },
+      { lat: area.south, lon: area.west },
+      { lat: area.south, lon: area.east },
+    ].map((corner) => distanceKm(center, corner)),
+  );
+}
+
 /** Great-circle distance in kilometers. */
 export function distanceKm(a, b) {
   const toRad = Math.PI / 180;