feat(dashboard): infinite scrolling for the prompt list, saved default plus session toggle

- PromptManagerConfig.INFINITE_SCROLL (web_ui.infinite_scroll) is reported
  and saved through the settings API; only booleans are accepted
- Settings modal gains an "Infinite Scrolling" default; saving applies it
  at once
- the results header gains an "Infinite scroll" checkbox that overrides the
  default for the current session without saving
- when on, the next page is appended as the list nears its bottom (same
  load-more rule as the gallery), page controls hide, a short page keeps
  loading until the list fills, and a refresh after an edit restarts from
  the top

web/admin.html

@@ -227,6 +227,11 @@
                                 </select>
                                 <span class="text-xs text-pm-secondary">per page</span>
                             </div>
+                            <!-- Session-only toggle; the saved default lives in Settings -->
+                            <label class="flex items-center gap-1.5 text-xs text-pm-secondary cursor-pointer" title="Load the next page as you scroll (this session)">
+                                <input type="checkbox" id="infiniteScrollSession" class="w-3.5 h-3.5 rounded border-pm bg-pm-input text-pm-accent focus:ring-pm-accent">
+                                Infinite scroll
+                            </label>
                         </div>
                         <span class="text-xs font-medium text-pm-secondary bg-pm-input px-2 py-0.5 rounded-full" id="resultsCount">Loading...</span>
                     </div>
@@ -413,6 +418,14 @@
                         </select>
                         <p class="text-xs text-pm-muted mt-1">Choose how the Web UI opens from ComfyUI nodes.</p>
                     </div>
+
+                    <div class="mt-3 flex items-center justify-between">
+                        <div>
+                            <label for="infiniteScrollDefault" class="block text-xs font-medium text-pm-secondary">Infinite Scrolling</label>
+                            <p class="text-xs text-pm-muted">Load the next page of prompts as you scroll. The checkbox in the list header overrides this for the current session.</p>
+                        </div>
+                        <input type="checkbox" id="infiniteScrollDefault" class="w-4 h-4 rounded border-pm bg-pm-input text-pm-accent focus:ring-pm-accent ml-3">
+                    </div>
                 </div>
 
                 <!-- Performance Section -->