feat: add info popovers to feed views

- Added info buttons to Most Recent, Subscriptions, History, Channel Profile, Search, and Explore views
- Attached popovers with descriptions of feed filtration methods
- Used `attachFeedInfoPopover` helper for consistent implementation
- Verified with Playwright script (verified popover visibility and text content)

views/subscriptions.html

@@ -1,6 +1,30 @@
 <!-- views/subscriptions.html -->
 <section data-ds="new">
-  <h2 class="mb-4 text-xl font-semibold text-text">Subscriptions</h2>
+  <div class="flex items-center gap-2 mb-4">
+    <h2 class="text-xl font-semibold text-text">Subscriptions</h2>
+    <button
+      type="button"
+      id="subscriptionsInfoTrigger"
+      class="text-muted hover:text-text focus:outline-none transition-colors"
+      aria-label="How is this feed sorted?"
+    >
+      <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="w-5 h-5"
+        aria-hidden="true"
+      >
+        <circle cx="12" cy="12" r="10"></circle>
+        <line x1="12" y1="16" x2="12" y2="12"></line>
+        <line x1="12" y1="8" x2="12.01" y2="8"></line>
+      </svg>
+    </button>
+  </div>
   <div id="subscriptionsVideoList" class="bv-grid-video">
     <div class="sidebar-loading-wrapper" role="status" aria-live="polite">
       <div class="sidebar-loading-indicator">