Series URL repair: owner-typed, gated by the poller's own fetch gate (#151)

backend/internal/web/templates/series-detail.html

@@ -1,9 +1,9 @@
 {{/* Per-Series page: one address per Series, keyed "<site>:<series_id>" so the
      list row is one hop from it. Everything here is a Series-level fact plus
-     the anonymous Reader count. The Check now control lands in its own .dform
-     below the .detail-grid; the correction form is the grid's first column,
-     and the grid's second waits for the series-URL repair (#151). The pending
-     and corrected markers ride the meta line with the other marks. */}}
+     the anonymous Reader count. Check now lands in its own .dform below the
+     .detail-grid; the correction form is the grid's first column and the URL
+     repair the second (issue #151). The pending and corrected markers ride the
+     meta line with the other marks. */}}
 {{define "series-detail"}}
 <a class="ghost detail-back" href="/admin/series">← Series</a>
 <h1 class="detail-title">{{.Title}}</h1>
@@ -20,6 +20,14 @@
       <button type="submit" class="ghost">Set</button>
     </div>
   </form>
+  <form class="dform" hx-post="/admin/series/{{.Key}}/series-url" hx-target="#detail-meta" hx-swap="outerHTML">
+    <h3>Repair series URL</h3>
+    <p class="hint">The Poll fetches this address — storing is not verifying it. A Site-wide host change is a SQL migration, not two hundred forms.</p>
+    <div class="field">
+      <input type="url" name="series_url" value="{{.URL}}" required>
+      <button type="submit" class="ghost">Set</button>
+    </div>
+  </form>
 </div>
 {{if .CanPoll}}
 <div class="dform">