fix(home): shelf honours the Plex gate; hero unpins its origin; palette asks for a surprise

- A13: with Plex off, the Home shelf and the hero's comfort tier go YouTube-only like the rails
  beside them (owner's call: hide the tiles). The pins are kept; GET /pins still lists them.
- Reorder deals the listed pins into the slots they already hold, so a partial list (hidden Plex
  pins, a stale tab) no longer puts two pins on one position; repeats are ignored.
- A21: a comfort hero carries `pinned_from`, the shelf entry it was resolved from; its menu acts on
  that pin, so a pinned show's next episode offers "Unpin" instead of creating a second pin.
- B12: the palette's "Meglepetés" asks for the surprise tier (the next press leading with it); the
  rotation carries on from there.
- B13: the surprise token names the history entry it was requested for (minted by setPage's new
  `then`, after the push) and is dropped on any other entry, so a navigation that never mounted
  Home cannot replay it later.

backend/app/routes/discover.py

@@ -13,7 +13,7 @@ from typing import Literal
 
 from fastapi import APIRouter, Depends
 from pydantic import BaseModel
-from sqlalchemy import select, update
+from sqlalchemy import select
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
 
@@ -53,7 +53,9 @@ def get_discover(
     `resume` and `shelf` are built once and handed to the hero, so the two rails the hero draws from
     are not queried twice for a single page load."""
     resume = rails.continue_watching(db, user)
-    shelf = pins.shelf(db, user)
+    # Plex off → the shelf rail (and so the hero's comfort tier) goes YouTube-only like the rails
+    # beside it; the pins are kept and `GET /pins` still lists them (`pins.shelf`).
+    shelf = pins.shelf(db, user, include_plex=rails.plex_available(db))
     return {
         "budget": budget,
         "hero": hero_mod.pick(db, user, budget, seed, resume=resume, shelf=shelf),
@@ -180,18 +182,11 @@ def reorder_pins(
     user: User = Depends(require_human),
     db: Session = Depends(get_db),
 ) -> dict:
-    """Rewrite the shelf order from a full list of pin ids.
+    """Rewrite the shelf order from the list of pin ids the client shows.
 
     Whole-list rather than a move-one delta: the shelf is short, and a full rewrite cannot leave two
-    tiles claiming the same slot the way an interrupted sequence of single moves can. Ids that are not
-    this user's are ignored rather than 404'd — a stale tab replaying an order that includes a pin
-    deleted meanwhile should reorder what still exists, not fail wholesale."""
-    owned = {p.id for p in pins.list_pins(db, user)}
-    for position, pin_id in enumerate(i for i in body.ids if i in owned):
-        db.execute(
-            update(ComfortPin)
-            .where(ComfortPin.id == pin_id, ComfortPin.user_id == user.id)
-            .values(position=position)
-        )
+    tiles claiming the same slot the way an interrupted sequence of single moves can. The list may be
+    PARTIAL (hidden Plex pins, a stale tab) — `pins.reorder` keeps what it leaves out in place."""
+    pins.reorder(db, user, body.ids)
     db.commit()
     return {"ok": True}