fix: escape single quotes in JS renderFlatList string

Haskell\'s \' within double-quoted string literals is interpreted as
just \' (no-op escape). Switched to \\' to produce \' in the JS
output, which correctly escapes the single quotes inside the
single-quoted JS string literal for the CSS class name.

src/Roux/Html.hs

@@ -254,7 +254,7 @@ searchJs =
         , ""
         , "function renderFlatList(items) {"
         , "  if (items.length === 0) return '<p>No recipes found.</p>';"
-        , "  let html = '<ul class=\'roux-recipes\'>';"
+        , "  let html = '<ul class=\\'roux-recipes\\'>';"
         , "  items.forEach(r => {"
         , "    html += '<li><a href=\"/recipes/' + encodeURIComponent(r.filename) + '\">' + escapeHtml(r.title) + '</a></li>';"
         , "  });"