fix(playlists): the table overflowed the page scroller

A truncate cell is white-space:nowrap, so its min-content width is the whole
title — under table-layout:auto the Title column grew until Length and the
remove button hung off the scroller (measured: table 1059px inside an 855px
wrapper, main.scrollWidth 1074 vs clientWidth 887). Fixed layout with a declared
width on every column but Title, which absorbs the rest.

frontend/src/components/Playlists.tsx

@@ -706,7 +706,10 @@ export default function Playlists() {
         >
           {/* Not clipped, so the header's filter popovers can overflow the table box. */}
           <div className="max-w-5xl">
-            <table className="w-full border-collapse text-sm">
+            {/* table-fixed, not auto: every column but the title has a declared width, so the
+                title absorbs the rest and its `truncate` works. Auto layout sizes columns from
+                min-content, and a nowrap title cell's min-content is the entire title. */}
+            <table className="w-full table-fixed border-collapse text-sm">
               <ColumnHead
                 columns={columns}
                 sort={viewSort}