Improve mobile responsive layout, add mobile stage switcher & collapsible filter bar

public/index.html

@@ -85,18 +85,23 @@
 
   <!-- NAVIGATION & STATS STRIP -->
   <nav class="subnav">
-    <div class="view-tabs" role="tablist">
-      <button type="button" class="view-tab active" data-view="board" role="tab">
-        📋 Pipeline Board
-      </button>
-      <button type="button" class="view-tab" data-view="grid" role="tab">
-        🗂️ Explorer & Mockup Gallery
-      </button>
-      <button type="button" class="view-tab" data-view="whack" role="tab">
-        🃏 Creative Whack Pack <span class="tab-pill">64 Cards</span>
-      </button>
-      <button type="button" class="view-tab" data-view="review" role="tab">
-        ⚔️ Review & Head-to-Head Arena
+    <div class="subnav-top-row">
+      <div class="view-tabs" role="tablist">
+        <button type="button" class="view-tab active" data-view="board" role="tab">
+          📋 Pipeline
+        </button>
+        <button type="button" class="view-tab" data-view="grid" role="tab">
+          🗂️ Explorer
+        </button>
+        <button type="button" class="view-tab" data-view="whack" role="tab">
+          🃏 Whack Pack <span class="tab-pill">64</span>
+        </button>
+        <button type="button" class="view-tab" data-view="review" role="tab">
+          ⚔️ Arena & Triage
+        </button>
+      </div>
+      <button type="button" id="btn-mobile-filter-toggle" class="btn btn-ghost btn-sm mobile-only">
+        🔍 Filters
       </button>
     </div>
 
@@ -135,7 +140,28 @@
   <main class="workspace">
     <!-- VIEW 1: PIPELINE KANBAN BOARD -->
     <section id="view-board" class="view-section active">
-      <div class="kanban-board" id="kanban-board">
+      <!-- Mobile Stage Switcher Pills -->
+      <div class="mobile-stage-switcher mobile-only" id="mobile-stage-switcher">
+        <button type="button" class="stage-tab active" data-mobile-stage="spark">
+          ✨ Spark <span class="stage-tab-count" id="mcount-spark">0</span>
+        </button>
+        <button type="button" class="stage-tab" data-mobile-stage="exploring">
+          🔍 Exploring <span class="stage-tab-count" id="mcount-exploring">0</span>
+        </button>
+        <button type="button" class="stage-tab" data-mobile-stage="building">
+          🛠️ Building <span class="stage-tab-count" id="mcount-building">0</span>
+        </button>
+        <button type="button" class="stage-tab" data-mobile-stage="shipped">
+          🚀 Shipped <span class="stage-tab-count" id="mcount-shipped">0</span>
+        </button>
+        <button type="button" class="stage-tab" data-mobile-stage="archived">
+          📦 Archived <span class="stage-tab-count" id="mcount-archived">0</span>
+        </button>
+        <button type="button" class="stage-tab" data-mobile-stage="all">
+          All
+        </button>
+      </div>
+      <div class="kanban-board" id="kanban-board" data-mobile-active-stage="spark">
         <div class="kanban-column" data-status="spark">
           <div class="kanban-col-header">
             <div>