Fix banner positioning: use above-main-outlet and adjust below-header width

- Replace above-main-container-outlet with above-main-outlet for proper #main-outlet placement
- Add CSS rule for below-site-header positioning with sidebar-aware width
- Set max-width to calc(var(--d-sidebar-width) + var(--d-max-width)) for below-header
- Update section class name from above-main-container-outlet to above-main-outlet
- Remove deprecated above-main-container-outlet connector directory

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

common/common.scss

@@ -21,6 +21,10 @@
       width: 100%;
       margin: 0 auto;
     }
+
+    .below-site-header.welcome-card {
+      max-width: calc(var(--d-sidebar-width, 0px) + var(--d-max-width, 1110px));
+    }
   }
   
   @media (max-width: 769px) {

javascripts/discourse/connectors/above-main-outlet/welcome-banner.hbs

@@ -1,6 +1,6 @@
 {{#if this.theme.enable_welcome_banner}}
 {{#unless (eq this.theme.banner_position "below_header")}}
-<section class="above-main-container-outlet welcome-card">
+<section class="above-main-outlet welcome-card">
     <div class="hero-section">
         <div class="hero-deco"></div>
         <div class="hero-content">