feat: show accumulated distance per gear item in gear tab

Compute total distance from allActivities where gear name matches and
display it inline next to each gear item. Also add gear field to
ActivitySummary type so index shard gear data is accessible in the UI.

site/src/lib/types.ts

@@ -69,6 +69,7 @@ export interface ActivitySummary {
   climbing_vam_mh?: number | null;
   climbing_time_s?: number | null;
   source: string | null;
+  gear: string | null;
   privacy: Privacy;
   detail_url: string | null;
   track_url: string | null;