feat(web): densify all-books and series grids

Book cards on the library (all-books) page were oversized at full
window width, and both the all-books and series grids showed only
2 columns on phones, making covers unnecessarily large on mobile.

Shift the all-books column ladder up one at every breakpoint
(2/4/5/6 -> 3/5/6/7) so the responsive reflow the grid is liked for
is preserved while every window size gets smaller cards; the series
grid gains a column at mobile only (2 -> 3), leaving md/lg untouched
per request. Dashboard carousel sizing (w-36/w-40) and the series
stacked-covers component are deliberately unchanged.

templ codegen and the tailwind build output commit with the source
change that produced them (repo convention).

templates/series.templ

@@ -170,7 +170,7 @@ templ Series(user User, seriesList []SeriesCardData, libData []LibraryData, curr
 							</div>
 						}
 					}
-					<div id="series-grid" class="grid grid-cols-2 md:grid-cols-4 lg:grid-cols-6 gap-6">
+					<div id="series-grid" class="grid grid-cols-3 md:grid-cols-4 lg:grid-cols-6 gap-6">
 						for _, series := range seriesList {
 							@SeriesCard(series)
 						}