E5 S7: Plex filter UI — listbox-select pickers + studio filter

Reworks the always-expanded filter chip walls into compact, Seerr-style
"+ Add" → searchable-popover pickers (the user's space-saving ask), and adds
the missing studio filter.

- New MultiSelectChips: selected values as removable chips + a "+ Add" trigger
  opening a searchable checklist (AnchoredPopover platform — menuitemcheckbox,
  arrow/Escape, anchor flip). Options carry facet counts; a large vocabulary
  renders a 50-row cap + "N more — refine with search" footer (studios run to
  ~1500). Replaces the flat Genre + Age-rating chip lists.
- New Studio filter via the same picker. Backend: /facets now aggregates the
  studio vocabulary (distinct studio + count, self-excluded like genres). The
  studio filter itself already existed (only addable from the detail page before).
- Collection converted to the same "+ Add" pattern (CollectionPicker): a
  single-select popover with server-side search + the 50-cap; the selected
  collection still shows as a removable chip. Retires the always-inline search+list.

New i18n plex.filter.studio/add/moreRefine + common.search/remove/noResults
(en+hu). Tests: MultiSelectChips.dom.test.tsx (5, incl. the cap) +
test_plex_facets studio-vocabulary. Browser-E2E'd: Genre→Horror(402),
Studio→A24(14, capped/searched), Collection→James Bond(26)/harry-search.
Gate: vitest 342, backend lane 403.

backend/app/routes/plex/browse.py

@@ -312,6 +312,7 @@ def facets(
     empty = {
         "genres": [],
         "content_ratings": [],
+        "studios": [],
         "year_min": None,
         "year_max": None,
         "rating_max": None,
@@ -355,6 +356,7 @@ def facets(
 
     genre_counts: dict[str, int] = {}
     cr_counts: dict[str, int] = {}
+    studio_counts: dict[str, int] = {}
     years: list[int] = []
     ratings: list[float] = []
     durs: list[int] = []
@@ -406,6 +408,21 @@ def facets(
         )
         for cr, c in db.execute(crq).all():
             cr_counts[cr] = cr_counts.get(cr, 0) + c
+        # Studios — exclude its own (each offered studio is a valid OR-addition that only widens).
+        stq = (
+            wsq(
+                select(model.studio, func.count()),
+                model,
+                ids,
+                {**p, "studios": None},
+                kind_movie,
+                True,
+            )
+            .where(model.studio.isnot(None))
+            .group_by(model.studio)
+        )
+        for s, c in db.execute(stq).all():
+            studio_counts[s] = studio_counts.get(s, 0) + c
         # Year bounds — exclude the year filter.
         by = db.execute(
             wsq(
@@ -460,6 +477,9 @@ def facets(
     # undo a zero-result selection. Count 0 is fine (genre chips don't display counts).
     for g in split_csv(f.genres):
         genre_counts.setdefault(g, 0)
+    # Same for the actively-selected studios, so a selected studio stays removable even at zero matches.
+    for s in split_csv(f.studios):
+        studio_counts.setdefault(s, 0)
     return {
         "genres": [
             {"value": g, "count": c}
@@ -469,6 +489,10 @@ def facets(
             {"value": cr, "count": c}
             for cr, c in sorted(cr_counts.items(), key=lambda kv: -kv[1])
         ],
+        "studios": [
+            {"value": s, "count": c}
+            for s, c in sorted(studio_counts.items(), key=lambda kv: (-kv[1], kv[0]))
+        ],
         "year_min": min(years) if years else None,
         "year_max": max(years) if years else None,
         "rating_max": max(ratings) if ratings else None,