feat(filters+ui): per-element author/publisher filters, playlist toggles, Up Next API, reorder UI, dashboard badges

Phases 4 + 5 of the metadata overhaul (plan §4, §5) plus §3 handler
wiring.

Filters (§4.1): author_filter/publisher_filter now match per-element
against the authors[]/publishers[] arrays — a co-authored book matches
any one of its authors — with comma-joined params acting as
OR-within-facet multi-select (string_to_array + cross unnest). Legacy
single-value params unchanged on the wire; series/genre/language
filters stay on their varchar columns; narrator filter already
per-element.

Collections API (§3.3-3.5): collection detail carries viewer +
hide_finished into the listing query and exposes up_next (visible-
library-enforced reading-queue head); PUT
/api/collections/:id/items/order (owner-only, full-order rewrite);
UpdateCollectionRequest gains hide_finished/show_up_next ([]
string last-value-wins for the hidden-false-sibling checkbox pattern)
merged server-side OVER stored view_settings so imported_from_series
provenance survives edits; EditCollectionModal renders the toggles
from view_settings.

Dashboard (§5.5): sections JSON carries is_playlist/complete
(dashboard.ts is the AGENTS-documented JSON-render exception; first
paint stays templ). Fully-read playlists render '✓ Playlist complete'
instead of an empty rail; imported playlists get a 📖 Playlist badge.

Frontend: book detail shows subtitle + full authors + Explicit badge;
edit modal gains subtitle, comma-separated authors/publishers (client-
split to arrays exactly like narrators), step=any series number,
explicit checkbox; collection book cards get playlist move ↑/↓ buttons
persisting the full order via the reorder endpoint (templ partial
re-render on failure — DOM order is client-local, API order is truth).

AGENTS.md gotcha #3 amended per plan §3.7: user collections are
dashboard sections by default; the show_on_dashboard premise is
retired.

Verified: full affected integration sweep green (pins widened for
up_next/is_playlist/complete — changelog entries in
docs/contract_pins.md); unit suite green; go build + templ + vite
green.

web/src/collections.ts

@@ -541,6 +541,7 @@ export {
   showAllIcons,
   testRule,
   toggleSelection,
+  moveCollectionBook,
 };
 
 Alpine.data("collections", () => ({
@@ -553,6 +554,7 @@ Alpine.data("collections", () => ({
   initializeCollectionWebSocket,
   initCollectionsPage,
   loadCollectionRules,
+  moveCollectionBook,
   navigateToCollection,
   populateIconGrid,
   selectColor,
@@ -594,3 +596,67 @@ Alpine.data("collections", () => ({
     this.pendingAction = null;
   },
 }));
+
+// A2c §3.2: playlist ordering — move a card one slot and persist the full
+// resulting order. The DOM cards are the server-rendered truth for CURRENT
+// order; the API is the truth for SAVED order. On failure the grid refresh
+// from the templ partial so the UI never lies.
+async function moveCollectionBook(
+  this: any,
+  mediaId: string,
+  direction: number,
+): Promise<void> {
+  const container = document.getElementById("books-container");
+  if (!container) return;
+  const cards = Array.from(
+    container.querySelectorAll<HTMLElement>(".collection-book-card"),
+  );
+  const index = cards.findIndex(
+    (c) => c.dataset.mediaId === mediaId,
+  );
+  const target = index + direction;
+  if (index < 0 || target < 0 || target >= cards.length) return;
+
+  // Optimistic DOM swap (client-local state until the API confirms).
+  if (direction < 0) {
+    container.insertBefore(cards[index], cards[target]);
+  } else {
+    container.insertBefore(cards[target], cards[index]);
+  }
+
+  const orderedIds = Array.from(
+    container.querySelectorAll<HTMLElement>(".collection-book-card"),
+  )
+    .map((c) => c.dataset.mediaId)
+    .filter((id): id is string => Boolean(id));
+
+  const token = localStorage.getItem("token");
+  if (!token) return;
+  try {
+    const response = await fetch(
+      `/api/collections/${getCollectionId()}/items/order`,
+      {
+        method: "PUT",
+        headers: {
+          Authorization: `Bearer ${token}`,
+          "Content-Type": "application/json",
+        },
+        body: JSON.stringify({ item_ids: orderedIds }),
+      },
+    );
+    if (!response.ok) {
+      showToast("Failed to save the new order", "error");
+      // Rendering ownership: the templ partial re-renders the true order.
+      const gridTarget = document.getElementById("books-container");
+      if (gridTarget && (window as any).htmx) {
+        (window as any).htmx.ajax(
+          "GET",
+          `/collections/${getCollectionId()}/books-grid${window.location.search.startsWith("?") ? window.location.search : ""}`,
+          { target: "#books-container", swap: "innerHTML" },
+        );
+      }
+    }
+  } catch {
+    showToast("Failed to save the new order", "error");
+  }
+}