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/Tooltip.tsx

@@ -2,22 +2,29 @@ import { useState, useSyncExternalStore } from "react";
 import { PopoverSurface, useAnchoredPopover } from "./AnchoredPopover";
 import { hintsEnabled, subscribeHints } from "../lib/hints";
 
-type Side = "top" | "bottom";
+type Side = "top" | "bottom" | "left" | "right";
 
-/** Wrap any element to show a short glass hint caption on hover — but only while the
+/** Wrap any element to show a short glass hint caption on hover — by default only while the
  *  app-wide hints toggle (Settings → Appearance) is on. Anchored by the R8 popover platform, so it
  *  is never clipped by an overflow/stacking ancestor, flips when the preferred side runs out of room
- *  and slides back inside the viewport near an edge. */
+ *  and slides back inside the viewport near an edge.
+ *  `always` bypasses the hints toggle (for a label that IS the primary affordance, e.g. the slim nav
+ *  rail's flyout names); `openDelay` waits before showing (a rest-on-the-icon feel). */
 export default function Tooltip({
   hint,
   side = "top",
+  always = false,
+  openDelay = 0,
   children,
 }: {
   hint: string;
   side?: Side;
+  always?: boolean;
+  openDelay?: number;
   children: React.ReactNode;
 }) {
-  const enabled = useSyncExternalStore(subscribeHints, hintsEnabled, hintsEnabled);
+  const hintsOn = useSyncExternalStore(subscribeHints, hintsEnabled, hintsEnabled);
+  const enabled = always || hintsOn;
   const [open, setOpen] = useState(false);
   const pop = useAnchoredPopover({
     open: open && enabled && !!hint,
@@ -25,9 +32,9 @@ export default function Tooltip({
     mode: "hover",
     placement: side,
     offset: 8,
-    // Show/hide on contact, as the pre-platform tooltip did — the platform's 120/140 ms hover-intent
-    // default suits interactive cards but makes a fast sweep across an icon row surface no hints.
-    hoverDelay: { open: 0, close: 0 },
+    // Show/hide on contact by default (as the pre-platform tooltip did); `openDelay` adds a
+    // rest-before-show for labels that shouldn't flash on a fast sweep across an icon row.
+    hoverDelay: { open: openDelay, close: 0 },
   });
 
   if (!enabled || !hint) return <>{children}</>;