feeds: "Most Zapped" sidebar tab ranked by zap totals (#47)

Trending-pattern clone ranked by sats from kind-9735 receipts:

- js/zapTotals.js: per-pointer receipt aggregation. The feed's metric getter
  returns the cached total and schedules a batched fetch (#a/#e chunks via
  the L1 SubscriptionManager) for unknown/stale pointers; amounts parse via
  nip57 bolt11 with the zap request's amount tag as fallback; receipts are
  deduped by id so re-fetches never double-count; zero-receipt answers are
  cached (2-min TTL).
- sorters.js: shared count-ranked sorter (metric desc, recency tie-break,
  author spread, trusted-muted sink); Trending delegates unchanged, Most
  Zapped ranks on runtime.getZapTotal.
- Full wiring: feed definition, view + info popover, change-signal re-rank
  (order settles as receipts stream in), sidebar link, viewManager registry,
  feedCoordinator case/loader, FEED_TYPES.MOST_ZAPPED, and a
  FEATURE_MOST_ZAPPED_FEED flag (default on; off hides the tab).

Co-Authored-By: Claude Fable 5 <[email protected]>

components/sidebar.html

@@ -76,6 +76,27 @@
             </svg>
             <span class="sidebar-text">Trending</span>
           </a>
+          <a
+            id="mostZappedLink"
+            href="#view=most-zapped"
+            class="sidebar-nav-link"
+            title="Most Zapped"
+          >
+            <svg
+              xmlns="http://www.w3.org/2000/svg"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              stroke-width="2"
+              stroke-linecap="round"
+              stroke-linejoin="round"
+              class="sidebar-icon"
+              aria-hidden="true"
+            >
+              <polygon points="13 2 3 14 12 14 11 22 21 10 12 10 13 2"></polygon>
+            </svg>
+            <span class="sidebar-text">Most Zapped</span>
+          </a>
           <a href="#view=most-recent-videos" class="sidebar-nav-link" title="Recently Added">
             <img
               src="assets/svg/globe-icon.svg"