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)

backend/app/routes/plex.py

@@ -373,8 +373,10 @@ def _meta_filter_conds(model, p: dict) -> list:
         conds.append(model.added_at >= cutoff)
     for d in _csv(p.get("directors")):  # AND
         conds.append(model.directors.contains([d]))
-    for a in _csv(p.get("actors")):  # AND
-        conds.append(model.cast_names.contains([a]))
+    alist = _csv(p.get("actors"))
+    if alist:  # AND (all) or OR (any) — default OR, mirroring genre_mode
+        ac = [model.cast_names.contains([a]) for a in alist]
+        conds.append(and_(*ac) if p.get("actor_mode") == "all" else or_(*ac))
     stds = _csv(p.get("studios"))
     if stds:  # OR
         conds.append(model.studio.in_(stds))
@@ -405,6 +407,7 @@ class LibraryFilters:
     added_within: str | None = None
     directors: str | None = None
     actors: str | None = None
+    actor_mode: str = "any"  # how multiple actors combine: any (OR, default) | all (AND)
     studios: str | None = None
     collection: str | None = None
 
@@ -415,7 +418,8 @@ class LibraryFilters:
             "year_max": self.year_max, "rating_min": self.rating_min,
             "duration_min": self.duration_min, "duration_max": self.duration_max,
             "added_within": self.added_within, "directors": self.directors,
-            "actors": self.actors, "studios": self.studios, "collection": self.collection,
+            "actors": self.actors, "actor_mode": self.actor_mode,
+            "studios": self.studios, "collection": self.collection,
         }