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/plex/cards.py

@@ -3,9 +3,24 @@ playlists, and detail views render. Extracted from routes/plex/browse.py so the
 lives beside the other Plex read-model modules (detail.py, query.py) rather than inside the
 router. Pure functions — no DB, no request state."""
 
+from typing import NamedTuple
+
 from app.models import PlexItem, PlexShow, PlexState
 
 
+class ShowState(NamedTuple):
+    """A show's watch state rolled up from its episodes, as its card carries it. `resumable`: an unwatched
+    episode has a resume point, the one the card's Continue resumes and its Restart replays from 0. A
+    show part watched with its next episode untouched has none: Continue and Restart would both play
+    that episode from its start, so the card offers Play alone."""
+
+    status: str
+    resumable: bool
+
+
+SHOW_NEW = ShowState("new", False)
+
+
 # A card's wide backdrop, for a rail's landscape tile or a crossfading hero — but ONLY when the item
 # actually has art. `thumb` is always emitted (its endpoint placeholders a missing poster), but an
 # `art` URL for an item with no `art_key` would resolve to a broken/blank image on every card that
@@ -54,7 +69,7 @@ def movie_card(it: PlexItem, st: PlexState | None, *, lang: str) -> dict:
     }
 
 
-def show_card(sh: PlexShow, status: str = "new", *, lang: str) -> dict:
+def show_card(sh: PlexShow, state: ShowState = SHOW_NEW, *, lang: str) -> dict:
     return {
         "id": sh.rating_key,
         "type": "show",
@@ -66,7 +81,8 @@ def show_card(sh: PlexShow, status: str = "new", *, lang: str) -> dict:
         "art": _art_url(sh.rating_key, sh.art_key),
         "season_count": sh.child_count,
         # Aggregate watch-state across the show's episodes (new | in_progress | watched) → grid badge.
-        "status": status,
+        "status": state.status,
+        "resumable": state.resumable,
     }