feat(series): multi-field search, sort-direction toggle, apply placement

Toolbar feedback round: the series search box now matches whatever the
main search matches for a group — series NAME, any book's AUTHOR, and
any book's TITLE inside the series (WHERE EXISTS per group-row, so
counts stay true); the separate author input is gone from the toolbar
(the author= param stays live for the JSON API and deep links). The
sort control becomes a base-key select (Date added/Name/Author/Books/
Progress/Last read) plus a chevron direction toggle that flips and
resubmits; sort/dir compose through ResolveSeriesSort (full registry
keys keep working for back-compat, unknown base keys fall to recent).
The search/apply button moved next to the search box as requested, and
default URLs stay clean (sort/dir only emitted once the user chooses).

web/src/series.ts

@@ -26,4 +26,14 @@ Alpine.data("seriesPage", () => ({
       onSwitch: navigateToSeries,
     });
   },
+
+  // flipSortDir inverts the direction hidden input and resubmits the
+  // plain-GET filter form (the URL stays the single source of truth).
+  flipSortDir() {
+    const input = this.$refs.sortDir as HTMLInputElement | undefined;
+    if (!input) return;
+    input.value = input.value === "asc" ? "desc" : "asc";
+    const form = input.closest("form") as HTMLFormElement | null;
+    if (form) form.requestSubmit();
+  },
 }));