fix: wrap hero and section-split MudGrids in plain HTML elements so CSS isolation scope attributes reach .hero and .section-split rules

DeepDrftPublic.Client/Pages/Home.razor

@@ -5,15 +5,21 @@
 <PageTitle>Deep DRFT - Electronic Music Collective</PageTitle>
 
 @* Hero - split 50/50 *@
-<MudGrid Spacing="0" Class="hero">
-    <MudItem xs="12" md="6" Class="hero-left">
+<section class="hero">
+    <MudGrid Spacing="0" Style="height: 100%;">
+        <MudItem xs="12" md="6">
+            <div class="hero-left">
                 <DeepDrftHero />
+            </div>
         </MudItem>
 
-    <MudItem xs="12" md="6" Class="hero-right">
+        <MudItem xs="12" md="6">
+            <div class="hero-right">
                 <NowPlaying />
+            </div>
         </MudItem>
     </MudGrid>
+</section>
 
 @* Divider *@
 <div class="section-divider">
@@ -24,7 +30,8 @@
 
 @* Sound section *@
 <section class="section">
-    <MudGrid Class="section-header-grid" Style="margin-bottom: 5rem;">
+    <div class="section-header-grid">
+        <MudGrid Style="margin-bottom: 5rem;">
             <MudItem xs="12" md="4">
                 <div class="section-label">Genres &amp; Moods</div>
                 <h2 class="section-title">Every<br /><em>Frequency</em><br />Explored</h2>
@@ -35,6 +42,7 @@
                 </p>
             </MudItem>
         </MudGrid>
+    </div>
 
     <div class="genre-grid">
         @* TODO Phase 2.2: wire each genre to /genres/{slug} *@
@@ -105,16 +113,20 @@
 </section>
 
 @* Split: origin + connect *@
-<MudGrid Spacing="0" Class="section-split">
-    <MudItem xs="12" md="6" Class="split-left">
+<div class="section-split">
+    <MudGrid Spacing="0" Style="height: 100%;">
+        <MudItem xs="12" md="6">
+            <div class="split-left">
                 <div class="split-eyebrow">Our Origin</div>
                 <h2 class="split-title">Where the Holy City<br /><em>Meets the Future</em></h2>
                 <p class="split-body">
                     Charleston, South Carolina holds centuries of culture in its streets. We carry that weight into the studio &mdash; tradition as tension against the forward pull of electronic sound. The result is music that feels both ancient and unimagined.
                 </p>
+            </div>
         </MudItem>
 
-    <MudItem xs="12" md="6" Class="split-right">
+        <MudItem xs="12" md="6">
+            <div class="split-right">
                 <div class="connect-label">Stay Connected</div>
                 <h2 class="connect-title">Never Miss<br />a <em>Session</em></h2>
                 <div class="connect-options">
@@ -140,8 +152,10 @@
                 </div>
                 @* TODO: subscription form lives behind this CTA *@
                 <button class="btn-primary connect-cta" type="button">Subscribe Free</button>
+            </div>
         </MudItem>
     </MudGrid>
+</div>
 
 @* CTA banner *@
 <section class="cta-banner">