fix(plex): Restart only where an episode has a resume point; the Surprise draw is re-read, not redrawn

Show cards carry resumable (ShowState, from the same rollup) so a part-watched
show whose next episode is untouched offers Play, not a Continue and a Restart
that do the same thing; plexStarted is the one rule for cards and menus. The
Surprise rail's key sits under the discover root: whatever refreshes the rails
re-reads the draw (keep=) with its watch state now, kept past the 5-minute gc,
and only the reshuffle deals. Closing the player refreshes the Discover rails.
A show card's play acts on the last click only, and only where it was made.

backend/app/routes/plex/browse.py

@@ -164,6 +164,7 @@ def unified_library(
                 cast(null(), Integer).label("season_count"),
                 func.coalesce(st.position_seconds, 0).label("position_seconds"),
                 m_status.label("status"),
+                literal(False).label("resumable"),
                 # "last watched" sort key: when the movie was last resumed, else when it was marked
                 # watched. NULL for never-touched movies → nullslast sinks them (see the sort dict).
                 func.coalesce(st.progress_updated_at, st.watched_at).label("last_watched"),
@@ -211,6 +212,8 @@ def unified_library(
                 PlexShow.child_count.label("season_count"),
                 literal(0).label("position_seconds"),
                 s_status.label("status"),
+                # An episode holds a resume point (`ShowState.resumable`, the card's Continue + Restart).
+                (inp > 0).label("resumable"),
                 # Show leg's "last watched": max(resume/watched time) across the show's episodes (see
                 # rollup.agg_subquery include_resumed). NULL for a never-watched show → nullslast.
                 agg.c.resumed_at.label("last_watched"),
@@ -276,6 +279,7 @@ def unified_library(
                         "thumb": f"/api/plex/image/{r.rk}",
                         "season_count": r.season_count,
                         "status": r.status,
+                        "resumable": r.resumable,
                     }
                 )