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>

styles.css

@@ -69,6 +69,10 @@ html.ns-authed #setup-screen{display:none}
 .header-search-wrap input{flex:1;min-width:0;background:none;border:none;outline:none;color:var(--text);font-family:var(--font);font-size:14px}
 .header-search-wrap input::placeholder{color:var(--text3)}
 
+#header-search-overlay{position:fixed;left:0;right:0;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:11;overflow-y:auto;max-height:calc(100vh - 120px)}
+@media(max-width:768px){#header-search-overlay{max-height:calc(100vh - var(--player-h) - 160px)}}
+@media(max-width:359px){#mobile-header .sidebar-logo span{display:none}}
+
 nav{flex:1;overflow-y:auto;padding:4px 10px}
 .nav-section{margin-bottom:18px}
 .nav-section-title{font-size:10px;font-weight:600;letter-spacing:1px;text-transform:uppercase;color:var(--text3);padding:0 8px;margin-bottom:3px}