feat: show pace (min/km) for running, hiking, walking, other activities

Cycling keeps km/h; pace sports show e.g. "5:30 /km" in the feed card,
activity stat panel (avg/max), and laps table.

site/src/components/ActivityFeed.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
   import { onMount } from 'svelte';
   import type { ActivitySummary, BASIndex, Sport } from '../lib/types';
-  import { formatDistance, formatDuration, formatElevation, formatDate, isUnlisted, sportIcon, sportColor, sportLabel } from '../lib/format';
+  import { formatDistance, formatDuration, formatElevation, formatDate, formatSpeed, formatPace, isPaceSport, isUnlisted, sportIcon, sportColor, sportLabel } from '../lib/format';
   import { loadIndexPaged, loadShardActivities, loadCombinedFeed } from '../lib/dataloader';
   import FeedMapView from './FeedMapView.svelte';
 
@@ -434,7 +434,7 @@
         {#if a.avg_speed_kmh || a.avg_hr_bpm}
           <div class="flex gap-4 mt-3 pt-3 border-t border-zinc-800 text-xs text-zinc-400">
             {#if a.avg_speed_kmh}
-              <span>⚡ {a.avg_speed_kmh.toFixed(1)} km/h</span>
+              <span>⚡ {isPaceSport(a.sport) ? formatPace(a.avg_speed_kmh) : formatSpeed(a.avg_speed_kmh)}</span>
             {/if}
             {#if a.avg_hr_bpm}
               <span>♥ {a.avg_hr_bpm} bpm</span>