feat(ux): card unification, slim icon nav, filter/plex fixes (7-item batch)

1A ChannelPage "Full history" button no longer wraps (whitespace-nowrap).
1B Extract the manager's press-and-hold priority stepper into a shared
   PriorityStepper and add it to the channel detail header (subscribed, non-demo);
   backend channel_detail now returns the per-subscription `priority`.
2  Unify YouTube + Plex media cards onto one look/behaviour: drop the whole-card
   hover LIFT (VideoCard) — which also fixes the clipped-top bug — and instead the
   inner thumbnail/poster ZOOMS on hover (both); give the flat Plex posters the same
   glass-card 3D depth + accent hover border as the feed cards (shadow-md is a
   transparent no-op here, so it's glass-card that provides the depth); clamp Plex
   card titles to a fixed 2-line height so 1- vs 2-line titles align.
3  Nav rail is now always a slim icon-only column, flush to the left edge; each icon
   reveals a floating name label on hover (Tooltip gains `always` + `openDelay`, and
   a right side). Removed the pin/unpin toggle, the expand-on-hover mode and the
   navCollapsed pref plumbing.
4  Scope the side-panel peek-open HOVER to the tab handle + the card (not the whole
   full-height slot next to the rail), so approaching the nav no longer pops the
   filter open; focus stays container-wide. useHoverFocusWithin gains a hover-out
   grace period + split hover/focus handler groups.
5  Plex art backdrop fills the whole viewport (a fixed inset-0 layer behind the
   transparent app) instead of only the inset <main> box.
6  Plex season binge continues across seasons: the season view's play queue now
   spans the whole show (allKeys), so a season's last episode rolls into the next
   season's first (seasonKeys stays for "add season to playlist").
7  When a Plex video/episode ends with nothing queued next, the player returns to
   the previous page (onEnded → onClose) instead of stranding a black screen.

frontend/src/components/SidePanel.tsx

@@ -46,7 +46,11 @@ export default function SidePanel({
     // Layout slot: reserves only the tab's gutter when unpinned, so the expanded card overlays
     // content instead of pushing it. Pinned reserves the full width (in-flow), as before.
     <div
-      {...peek.handlers}
+      // Focus is tracked container-wide (keyboard: tab anywhere inside holds it open). HOVER is NOT
+      // on this full-height slot — that made the whole column next to the nav rail a live target, so
+      // merely approaching the rail popped the panel open. Hover now lives only on the visible tab
+      // handle + the expanded card below, so only pointing AT the tab opens it.
+      {...peek.focusHandlers}
       className={`hidden md:block relative shrink-0 transition-[width] ${pinned ? "w-67" : "w-9"}`}
     >
       {/* The tab: a small handle flush against the nav rail, flat on the docked edge. It stays
@@ -56,6 +60,7 @@ export default function SidePanel({
           this square-cornered tab sits right under that arc, so it would otherwise bleed through.
           `opacity-0` (not `invisible`/`hidden`) keeps it hoverable and focusable. */}
       <button
+        {...peek.hoverHandlers}
         onClick={onToggleCollapse}
         aria-label={pinned ? t("sidebar.unpin") : t("sidebar.pin")}
         className={`glass glass-hover absolute top-3 left-0 z-paneltab flex flex-col items-center gap-2 px-1.5 py-3 rounded-l-none rounded-r-xl transition-opacity ${
@@ -77,7 +82,10 @@ export default function SidePanel({
       </button>
 
       {expanded && (
-        <aside className="glass absolute top-3 bottom-3 left-0 z-panel w-64 rounded-2xl flex flex-col overflow-hidden">
+        <aside
+          {...peek.hoverHandlers}
+          className="glass absolute top-3 bottom-3 left-0 z-panel w-64 rounded-2xl flex flex-col overflow-hidden"
+        >
           {/* Row 1 — identity only: pin, icon, title (flexes + truncates last), count, customize.
               Module actions live on their own row below so the title always has room. */}
           <div className="flex items-center gap-1.5 px-3 py-2.5 border-b border-border/60 flex-none">