1 — Timeseries split

- writer.py: timeseries is now written to {id}.timeseries.json as a separate file. The detail JSON gets a timeseries_url field instead. finalize_pending and cleanup_pending handle the extra file.
  - merge.py (merge_one): symlinks the .timeseries.json file alongside the detail JSON. merge_all already handles it transparently (the .timeseries.json stem doesn't match any activity
  ID in to_merge, so it falls through to the symlink branch).
  - types.ts: timeseries is now timeseries?: Timeseries | null, and timeseries_url?: string | null added.
  - dataloader.ts: new loadTimeseries(url, detailUrl, base) function that resolves paths correctly in both single- and multi-user modes (uses the fetched detail URL's directory as the base).
  - ActivityDetail.svelte: loads timeseries separately after detail loads; uses detail.timeseries for IDB activities (embedded) or fetches via detail.timeseries_url for server activities. Charts show a pulse placeholder while loading.

 2 — GZip

  - GZipMiddleware (min 1 KB) added to both bincio/serve/server.py and bincio/edit/server.py — all API JSON responses are now gzip-compressed.
  - For static files (the big timeseries JSONs), nginx should be configured with gzip on; gzip_types application/json application/geo+json; — no code change needed on the server side.

  Net effect: opening an activity page now fetches ~1.4 KB (detail) instead of ~586 KB. The timeseries fetches ~60–150 KB gzip-compressed shortly after (it loads concurrently with the map rendering).

site/src/components/ActivityDetail.svelte

@@ -2,12 +2,12 @@
   import { onMount } from 'svelte';
   import { marked } from 'marked';
   import DOMPurify from 'dompurify';
-  import type { ActivitySummary, ActivityDetail, AthleteZones } from '../lib/types';
+  import type { ActivitySummary, ActivityDetail, AthleteZones, Timeseries } from '../lib/types';
   import { formatDistance, formatDuration, formatElevation, formatSpeed, formatDate, formatTime, sportIcon, sportLabel, sportColor } from '../lib/format';
   import ActivityMap from './ActivityMap.svelte';
   import ActivityCharts from './ActivityCharts.svelte';
   import EditDrawer from './EditDrawer.svelte';
-  import { loadActivity } from '../lib/dataloader';
+  import { loadActivity, loadTimeseries } from '../lib/dataloader';
 
   export let activity: ActivitySummary;
   export let base: string = '/';
@@ -17,6 +17,8 @@
   const editEnabled = editUrl !== '' || import.meta.env.PUBLIC_EDIT_ENABLED === 'true';
 
   let detail: ActivityDetail | null = null;
+  let timeseries: Timeseries | null = null;
+  let timeseriesLoading = false;
   let error = '';
   let hoveredIdx: number | null = null;
   let editOpen = false;
@@ -31,8 +33,17 @@
     try {
       detail = await loadActivity(activity.id, activity.detail_url ?? '', base);
       if (!detail) throw new Error('Activity not found');
+      // Use embedded timeseries (IDB activities) or lazy-fetch from URL
+      if (detail.timeseries) {
+        timeseries = detail.timeseries;
+      } else if (detail.timeseries_url) {
+        timeseriesLoading = true;
+        timeseries = await loadTimeseries(detail.timeseries_url, activity.detail_url ?? '', base);
+        timeseriesLoading = false;
+      }
     } catch (e: any) {
       error = e.message;
+      timeseriesLoading = false;
     }
   });
 
@@ -231,7 +242,7 @@
     {#if trackUrl}
       <ActivityMap
         {trackUrl}
-        timeseries={detail?.timeseries ?? null}
+        {timeseries}
         bbox={detail?.bbox ?? null}
         accentColor={color}
         bind:hoveredIdx
@@ -263,11 +274,11 @@
 <!-- Charts -->
 {#if error}
   <p class="text-red-400 text-sm mt-4">{error}</p>
-{:else if detail?.timeseries && detail.timeseries.t.length > 0}
+{:else if timeseries && timeseries.t.length > 0}
   <div class="bg-zinc-900 rounded-xl border border-zinc-800 p-4">
-    <ActivityCharts timeseries={detail.timeseries} bind:hoveredIdx {athlete} />
+    <ActivityCharts {timeseries} bind:hoveredIdx {athlete} />
   </div>
-{:else if !detail}
+{:else if !detail || timeseriesLoading}
   <div class="bg-zinc-900 rounded-xl border border-zinc-800 p-4 h-32 animate-pulse"></div>
 {/if}