fix: view dropdown menu appears off-screen - add position: relative

The .view-dropdown__menu uses position: absolute; top: calc(100% + 4px)
which needs a positioned ancestor. The .view-dropdown CSS class provided
position: relative, but the <view-dropdown> custom element had no class —
so the menu resolved against the viewport and rendered 581px off-screen.
Fixed by adding position: relative to the .view-dropdown element selector.

muxplex/frontend/style.css

@@ -63,7 +63,7 @@ session-grid,
 session-tile,
 sidebar-item { display: contents; }
 
-view-dropdown { display: block; }
+view-dropdown { display: block; position: relative; }
 
 /* Inline SVG icons — ensure consistent vertical alignment */
 .header-btn svg,