upload: add overwrite option to replace existing activities

When 'Overwrite existing activities' is checked, duplicate activities are
re-extracted and replaced instead of silently skipped:
- Deletes {id}.json, .geojson, .timeseries.json from activities/ and _merged/
- Removes the stale index summary and dedup cache entry
- Ingests the new file fresh via ingest_parsed
- Reports 'overwritten' (↺) status in the SSE stream vs 'imported' (↓)
- done event includes 'overwritten' count; UI shows it alongside 'added'

site/src/layouts/Base.astro

@@ -317,6 +317,17 @@ try {
               <span class="text-zinc-600 block mt-0.5">Lets you reprocess if the format changes. See the <a href={`${baseUrl}about/`} class="underline hover:text-zinc-400">About page</a> for details.</span>
             </span>
           </label>
+          <label class="flex items-start gap-2 mt-2 cursor-pointer group">
+            <input
+              id="upload-overwrite"
+              type="checkbox"
+              class="mt-0.5 accent-amber-500 shrink-0"
+            />
+            <span class="text-xs text-zinc-500 group-hover:text-zinc-300 transition-colors leading-snug">
+              Overwrite existing activities
+              <span class="text-zinc-600 block mt-0.5">Re-extract and replace any duplicate found on the server. Use to fix a corrupted or mis-parsed activity.</span>
+            </span>
+          </label>
           <p id="upload-status" class="mt-3 text-xs text-center" style="color: var(--text-5); min-height: 1.25rem"></p>
         </div>
 
@@ -554,6 +565,7 @@ try {
       const input             = document.getElementById('upload-input');
       const label             = document.getElementById('upload-label');
       const keepOriginalChk   = document.getElementById('upload-keep-original');
+      const overwriteChk      = document.getElementById('upload-overwrite');
       const fileStatus        = document.getElementById('upload-status');
       const stravaStatus  = document.getElementById('strava-status');
       const stravaConnect = document.getElementById('strava-connect-area');
@@ -629,6 +641,7 @@ try {
         const fd = new FormData();
         for (const f of files) fd.append('files', f);
         fd.append('store_original', keepOriginalChk?.checked ? 'true' : 'false');
+        fd.append('overwrite', overwriteChk?.checked ? 'true' : 'false');
 
         const xhr = new XMLHttpRequest();
         xhr.open('POST', `${editUrl}/api/upload`);
@@ -636,7 +649,7 @@ try {
         xhr.setRequestHeader('Accept', 'text/event-stream');
 
         let buf = '';
-        let added = 0, dupes = 0, errors = 0, csvUpdates = 0;
+        let added = 0, overwrittenCount = 0, dupes = 0, errors = 0, csvUpdates = 0;
 
         xhr.onprogress = () => {
           const newText = xhr.responseText.slice(buf.length);
@@ -647,23 +660,25 @@ try {
               const ev = JSON.parse(line.slice(6));
               if (ev.type === 'progress') {
                 const pct = Math.round((ev.n / ev.total) * 100);
-                const icon = ev.status === 'imported' ? '↓' : ev.status === 'duplicate' ? '·' : '✗';
+                const icon = ev.status === 'imported' ? '↓' : ev.status === 'overwritten' ? '↺' : ev.status === 'duplicate' ? '·' : '✗';
                 fileStatus.textContent = `${icon} ${ev.n}/${ev.total} (${pct}%) — ${ev.name}`;
                 if (ev.status === 'imported') added++;
+                else if (ev.status === 'overwritten') overwrittenCount++;
                 else if (ev.status === 'duplicate') dupes++;
                 else errors++;
               } else if (ev.type === 'csv') {
                 csvUpdates = ev.updates;
               } else if (ev.type === 'done') {
-                added = ev.added; dupes = ev.duplicates; errors = ev.errors; csvUpdates = ev.csv_updates;
+                added = ev.added; overwrittenCount = ev.overwritten ?? 0; dupes = ev.duplicates; errors = ev.errors; csvUpdates = ev.csv_updates;
                 const parts = [];
                 if (added > 0) parts.push(`${added} added`);
+                if (overwrittenCount > 0) parts.push(`${overwrittenCount} overwritten`);
                 if (csvUpdates > 0) parts.push(`${csvUpdates} updated from CSV`);
                 if (dupes) parts.push(`${dupes} duplicate${dupes > 1 ? 's' : ''}`);
                 if (errors) parts.push(`${errors} failed`);
                 if (parts.length === 0) parts.push('nothing to add');
                 fileStatus.textContent = parts.join(', ');
-                const anyGood = added > 0 || csvUpdates > 0;
+                const anyGood = added > 0 || overwrittenCount > 0 || csvUpdates > 0;
                 fileStatus.style.color = anyGood ? '#4ade80' : '#a1a1aa';
                 if (anyGood) setTimeout(() => window.location.reload(), 1200);
                 else drop.style.pointerEvents = '';