feat(plex): actor filter AND/OR toggle (default OR) (S2)

Multiple selected actors now combine as OR (any) by default — click several cast
and see films featuring ANY of them — instead of the old hardcoded AND that
emptied the grid. An AND (all) toggle in the ACTIVE filter section (shown for 2+
actors, mirroring the genre match toggle) narrows to films with ALL of them.
Backend actor_mode param mirrors genre_mode. Verified: OR John Goodman|Douglas
M. Griffin = 11 films; AND = 1 (10 Cloverfield Lane). (Plex cast-explore S2)

frontend/src/lib/api.ts

@@ -840,7 +840,8 @@ export interface PlexFilters {
   durationMax?: number | null;
   addedWithin?: string; // "" | "24h" | "1w" | "1m" | "6m" | "1y"
   directors: string[]; // AND — titles featuring ALL selected
-  actors: string[]; // AND — titles featuring ALL selected
+  actors: string[]; // OR (any) by default, or AND (all) via actorMode
+  actorMode?: "any" | "all"; // how multiple actors combine (default any = OR)
   studios: string[]; // OR — from any selected studio
   collection?: string | null; // a single Plex collection (rating_key)
   collectionTitle?: string | null; // its title, for the active-filter chip
@@ -882,6 +883,7 @@ function appendPlexFilters(u: URLSearchParams, f: PlexFilters): void {
   if (f.addedWithin) u.set("added_within", f.addedWithin);
   if (f.directors?.length) u.set("directors", f.directors.join(","));
   if (f.actors?.length) u.set("actors", f.actors.join(","));
+  if (f.actorMode === "all") u.set("actor_mode", "all");
   if (f.studios?.length) u.set("studios", f.studios.join(","));
   if (f.collection) u.set("collection", f.collection);
 }