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/components/PlexSidebar.tsx

@@ -211,6 +211,23 @@ export default function PlexSidebar({
                     onRemove={() => patch({ directors: filters.directors.filter((x) => x !== d) })}
                   />
                 ))}
+                {filters.actors.length > 1 && (
+                  <div className="w-full inline-flex overflow-hidden rounded-lg border border-border text-[11px]">
+                    {(["any", "all"] as const).map((m) => (
+                      <button
+                        key={m}
+                        onClick={() => patch({ actorMode: m })}
+                        className={`px-2 py-0.5 transition ${
+                          (filters.actorMode ?? "any") === m
+                            ? "bg-accent text-accent-fg"
+                            : "text-muted hover:bg-surface"
+                        }`}
+                      >
+                        {t(`plex.filter.match.${m}`)}
+                      </button>
+                    ))}
+                  </div>
+                )}
                 {filters.actors.map((a) => (
                   <RemovableChip
                     key={`a:${a}`}