fix: header search overlay clipping and mobile fit

- Change overlay from position:absolute to position:fixed so it isn't
  clipped by main-content's overflow-y:auto
- Set overlay top dynamically from header.offsetHeight so it always
  anchors exactly below the sticky header
- Responsive max-height: accounts for player bar + bottom nav on mobile
- Hide logo text on ≤359px screens to keep search pill wide enough

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.html

@@ -123,7 +123,7 @@
             </button>
           </div>
         </div>
-        <div id="header-search-overlay" style="display:none;position:absolute;left:0;right:0;top:100%;max-height:calc(100vh - 100px);overflow-y:auto;background:var(--bg);border-bottom:1px solid var(--border);box-shadow:0 12px 32px rgba(0,0,0,.5);padding:6px 12px 20px;z-index:9">
+        <div id="header-search-overlay" style="display:none">
           <div id="header-search-results"></div>
         </div>
       </div>