fix: image refs in description and broken gallery URLs

- EditDrawer: stop auto-inserting ![filename](...) into description on
  upload — images are tracked via custom.images; the refs only cluttered
  the textarea. Strip any pre-existing refs on load so old sidecars are
  also cleaned up when the drawer is opened.
- ActivityDetail: imageBase now treats detail_url that starts with '/'
  as already-absolute (same fix pattern as track_url / detail_url);
  was prepending ${base}data/ on top of /data/... → double path.

site/src/components/ActivityDetail.svelte

@@ -82,10 +82,11 @@
   })();
 
   // Derive image dir from detail_url so multi-user paths resolve correctly.
-  // "dave/_merged/activities/foo.json" → "/data/dave/_merged/activities/images/{id}/"
+  // Relative: "dave/_merged/activities/foo.json" → "/data/dave/_merged/activities/images/{id}/"
+  // Absolute: "/data/dave/_merged/activities/foo.json" → "/data/dave/_merged/activities/images/{id}/"
   $: imageBase = (() => {
     const du = activity.detail_url ?? '';
-    const dir = du.startsWith('http')
+    const dir = du.startsWith('http') || du.startsWith('/')
       ? du.substring(0, du.lastIndexOf('/') + 1)
       : du.includes('/')
         ? `${base}data/${du.substring(0, du.lastIndexOf('/') + 1)}`

site/src/components/EditDrawer.svelte

@@ -51,7 +51,8 @@
       title       = d.title       ?? '';
       sport       = d.sport       ?? 'cycling';
       gear        = d.gear        ?? '';
-      description = d.description ?? '';
+      // Strip any auto-inserted image markdown refs — images are tracked via custom.images
+      description = (d.description ?? '').replace(/!\[[^\]]*\]\([^)]+\)\n?/g, '').trim();
       highlight   = d.highlight   ?? false;
       isPrivate   = d.private     ?? false;
       hideStats   = d.hide_stats  ?? [];
@@ -95,9 +96,6 @@
         if (res.ok) {
           const d = await res.json();
           if (!images.includes(d.filename)) images = [...images, d.filename];
-          // Insert markdown reference at cursor or end
-          const ref = `\n![${d.filename.replace(/\.[^.]+$/, '')}](${d.filename})`;
-          description = description.trimEnd() + ref;
         }
       }
     } catch (e: any) {
@@ -111,9 +109,6 @@
   async function deleteImage(filename: string) {
     await fetch(`${api}/images/${encodeURIComponent(filename)}`, { method: 'DELETE' });
     images = images.filter(f => f !== filename);
-    // Remove the markdown reference — escape filename before using in regex
-    const escaped = filename.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
-    description = description.replace(new RegExp(`!\\[[^\\]]*\\]\\(${escaped}\\)`, 'g'), '').trim();
   }
 
   function toggleStat(key: string) {