refactor(plex): dedup movie/show watch-state predicates into query.py (E3 S1)

The `show` scope (all|watched|in_progress|unwatched) filter and the status CASE
were hand-duplicated between unified_library (the grid) and facets.wsq — the
exact drift risk the review flagged (a hidden movie kept out of the grid must
not inflate facets). Extract them into four shared query.py helpers
(movie_status_case, show_status_case, apply_movie_state_filter,
apply_show_state_filter), model-agnostic (callers pass the joined state
expressions), and point all three call sites at them.

Pure behaviour-equivalence refactor: browse.py -67 lines, no query changes.
Green under the E3 S1 parity net + query_conversion/facets/field-scoped/lang
tests (348 DB-lane pass, ruff clean).

backend/app/routes/plex/browse.py

@@ -11,7 +11,6 @@ from sqlalchemy import (
     Integer,
     String,
     and_,
-    case,
     cast,
     delete,
     func,
@@ -50,10 +49,14 @@ from app.plex.query import (
     TS_CONFIG,
     LibraryFilters,
     apply_meta_filters,
+    apply_movie_state_filter,
+    apply_show_state_filter,
     field_recheck,
     genres_col,
     like_escape,
     meta_filter_conds,
+    movie_status_case,
+    show_status_case,
     split_csv,
     title_col,
     vector_col,
@@ -154,17 +157,7 @@ def unified_library(
     selects = []
     if want_movies and grid_field:
         st = aliased(PlexState)
-        m_status = case(
-            (st.status == "watched", "watched"),
-            (
-                and_(
-                    st.position_seconds > 0,
-                    or_(st.status.is_(None), st.status != "watched"),
-                ),
-                "in_progress",
-            ),
-            else_="new",
-        )
+        m_status = movie_status_case(st)
         mq = (
             select(
                 PlexItem.rating_key.label("rk"),
@@ -188,19 +181,7 @@ def unified_library(
             .outerjoin(st, and_(st.item_id == PlexItem.id, st.user_id == user.id))
             .where(PlexItem.kind == "movie", PlexItem.library_id.in_(movie_lib_ids))
         )
-        if show == "watched":
-            mq = mq.where(st.status == "watched")
-        elif show == "in_progress":
-            mq = mq.where(
-                st.position_seconds > 0,
-                or_(st.status.is_(None), st.status != "watched"),
-            )
-        elif show == "unwatched":
-            mq = mq.where(
-                or_(st.status.is_(None), st.status.notin_(["watched", "hidden"]))
-            )
-        else:
-            mq = mq.where(or_(st.status.is_(None), st.status != "hidden"))
+        mq = apply_movie_state_filter(mq, st, show)
         mq = apply_meta_filters(mq, PlexItem, p, lang)
         if f.duration_min is not None:
             mq = mq.where(PlexItem.duration_s >= f.duration_min)
@@ -216,11 +197,7 @@ def unified_library(
         tot = func.coalesce(agg.c.total, 0)
         wat = func.coalesce(agg.c.watched, 0)
         inp = func.coalesce(agg.c.inprog, 0)
-        s_status = case(
-            (and_(tot > 0, wat >= tot), "watched"),
-            (or_(wat > 0, inp > 0), "in_progress"),
-            else_="new",
-        )
+        s_status = show_status_case(tot, wat, inp)
         sq = (
             select(
                 PlexShow.rating_key.label("rk"),
@@ -244,12 +221,7 @@ def unified_library(
             .outerjoin(agg, agg.c.show_id == PlexShow.id)
             .where(PlexShow.library_id.in_(show_lib_ids))
         )
-        if show == "watched":
-            sq = sq.where(tot > 0, wat >= tot)
-        elif show == "in_progress":
-            sq = sq.where(or_(wat > 0, inp > 0), wat < tot)
-        elif show == "unwatched":
-            sq = sq.where(wat == 0, inp == 0)
+        sq = apply_show_state_filter(sq, tot, wat, inp, show)
         sq = apply_meta_filters(sq, PlexShow, p, lang)
         if tsq is not None:
             sq = sq.where(vector_match(PlexShow, lang, tsq))
@@ -393,23 +365,11 @@ def facets(
                 query = query.where(model.duration_s >= pp["duration_min"])
             if with_dur and pp.get("duration_max") is not None:
                 query = query.where(model.duration_s <= pp["duration_max"])
-            # Always join watch-state and mirror the grid's status branches (unified_library) exactly —
+            # Join watch-state and reuse the grid's exact movie state filter (unified_library) —
             # hidden movies never appear in the grid, so they must not inflate facet counts/bounds either.
             st = aliased(PlexState)
             query = query.outerjoin(st, and_(st.item_id == model.id, st.user_id == uid))
-            if show == "watched":
-                query = query.where(st.status == "watched")
-            elif show == "in_progress":
-                query = query.where(
-                    st.position_seconds > 0,
-                    or_(st.status.is_(None), st.status != "watched"),
-                )
-            elif show == "unwatched":
-                query = query.where(
-                    or_(st.status.is_(None), st.status.notin_(["watched", "hidden"]))
-                )
-            else:
-                query = query.where(or_(st.status.is_(None), st.status != "hidden"))
+            query = apply_movie_state_filter(query, st, show)
         else:
             if show in ("watched", "in_progress", "unwatched"):
                 agg = rollup.agg_subquery(db, uid).subquery()
@@ -417,12 +377,7 @@ def facets(
                 tot = func.coalesce(agg.c.total, 0)
                 wat = func.coalesce(agg.c.watched, 0)
                 inp = func.coalesce(agg.c.inprog, 0)
-                if show == "watched":
-                    query = query.where(tot > 0, wat >= tot)
-                elif show == "in_progress":
-                    query = query.where(or_(wat > 0, inp > 0), wat < tot)
-                else:
-                    query = query.where(wat == 0, inp == 0)
+                query = apply_show_state_filter(query, tot, wat, inp, show)
         return query
 
     genre_counts: dict[str, int] = {}