fix(live-tv): keep a hidden channel list discoverable and scoped per surface

The second report in #1458 ("all channels disappear after clearing the
playback history, reset does not bring them back") was not data loss: the
history write never touches playlist items. The reporter's screenshot shows
a collapsed channel rail, a state persisted under one localStorage key
shared by the M3U player, the Xtream/Stalker live layouts and the
favorites/recent live tab. It survived restart, "Remove all playlists" and
re-import, and the only way back was a 32px chevron or Ctrl/Cmd+B.

- LiveLayoutSidebarStateService keeps the state per surface (m3u / portal /
  collection) under live-sidebar-state:<surface>; the M3U player now goes
  through the service instead of its own signal. The legacy shared key is
  forgotten on startup and never read, so the update itself restores the
  list for everyone who got stuck.
- The workspace header renders a view_sidebar toggle on every route that
  renders its own rail (M3U all/groups, Xtream live, Stalker itv/radio), so
  the control exists in both states instead of disappearing with the rail.
  Collection pages keep their own toggle beside the content switch.
- While the rail is collapsed and nothing plays, every live host shows
  app-channel-list-hidden-state (title, shortcut hint, full-size "Show
  channels list" button) instead of asking to pick from a list that is not
  on screen. app-portal-empty-state gained optional hint/action inputs.
- New LAYOUT.CHANNELS_LIST_HIDDEN(_HINT) strings in en plus 18 locales.

Tests: service, empty-state, hidden-state and header component specs, a
separate video-player-sidebar spec (the main M3U spec sits at the test
line budget), and an Electron E2E covering history clearing, restore via
button/header/shortcut across restart and re-import, per-surface scoping
against an Xtream portal, and legacy-key cleanup.

Refs #1458

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture/iptvnator-ui-guidelines.md

@@ -216,8 +216,8 @@ remain local when the meaning is explicit.
 
 ### Collapsible Live Sidebar
 
-- M3U, Xtream, and Stalker live layouts share a single sidebar collapse toggle
-  that hides the channels rail to give the player and EPG full width.
+- M3U, Xtream, and Stalker live layouts share a sidebar collapse toggle that
+  hides the channels rail to give the player and EPG full width.
 - Xtream Live TV's root view (`/live` with no selected category) follows the
   same paginated `All Items` shell as VOD and Series: a widget header with the
   total channel count, page-size controls, and page navigation above the shared
@@ -234,15 +234,39 @@ remain local when the meaning is explicit.
   is `live` (Xtream) or `itv`/`radio` (Stalker); movies, series, favorites,
   and recent routes leave it untouched.
 - Collapsed state is owned by `LiveLayoutSidebarStateService`
-  (`providedIn: 'root'`) in `@iptvnator/portal/shared/util`. Every surface that
-  participates injects the service and reads `isCollapsed`; any toggle calls
-  `service.toggle()`. Persistence delegates to the existing
-  `live-sidebar-state` helpers, so the localStorage key stays unchanged and
-  missing/invalid values restore to expanded.
-- A `mat-icon-button` with `chevron_left` lives in the sidebar header and
-  toggles state. While collapsed, a floating `chevron_right` mini-fab appears
-  at the left edge of `.content-container` to restore the rail (and the
-  categories rail, in Xtream/Stalker live).
+  (`providedIn: 'root'`) in `@iptvnator/portal/shared/util` and kept **per
+  surface** (`LiveSidebarSurface`): `m3u` (the M3U player), `portal` (Xtream
+  and Stalker live layouts plus the shell categories rail) and `collection`
+  (the unified favorites/recent live tab). Every participant injects the
+  service, holds `isCollapsedFor(surface)` (a stable signal) and calls
+  `toggle(surface)`; nothing reads localStorage directly. Persistence lives
+  under `live-sidebar-state:<surface>`. Hiding the list is a per-context
+  choice: it must not follow the user from a portal to an M3U playlist, nor
+  from the desktop rail to the phone bottom drawer of another surface. The
+  pre-split shared key `live-sidebar-state` is forgotten on service
+  construction and never read — a stored `collapsed` there hid every channel
+  list in the app behind a 32px chevron and survived restart, "Remove all
+  playlists" and re-import (issue #1458).
+- The control never moves. Inside the rail a `mat-icon-button` with
+  `chevron_left` hides it; while collapsed a floating `chevron_right` mini-fab
+  sits at the left edge of `.content-container`. Because both of those live
+  in the thing they hide, the workspace header additionally renders
+  `view_sidebar` (`headerSidebarToggle`, `WorkspaceShellHeaderService`) on
+  every route that renders its own rail — M3U `all`/`groups`, Xtream `live`,
+  Stalker `itv`/`radio` (`resolveRouteLiveSidebarSurface`). It stays in place
+  in both states, uses `aria-pressed` (pressed = rail visible) and tints
+  primary only while the rail is hidden, since the hidden state is the
+  exception that deserves the cue. Collection pages are deliberately excluded:
+  only the page knows whether its live tab, and therefore the rail, is on
+  screen, so its own header toggle beside the content switch stays the owner.
+- While the rail is collapsed and nothing is playing, every live host renders
+  `app-channel-list-hidden-state` (`@iptvnator/portal/shared/ui`) instead of
+  the "select a channel" empty state: a title that says the list is hidden, a
+  one-line hint naming the shortcut, and a full-size "Show channels list"
+  stroked button wired to the same toggle. The generic
+  `app-portal-empty-state` grew optional `hint`, `actionLabel`, `actionIcon`
+  inputs and an `action` output for this; the action keeps full opacity while
+  icon and copy stay muted, because it is the way out of the state.
 - Keyboard shortcut: `Cmd/Ctrl+B`. The handler ignores events that originate
   inside `<input>`, `<textarea>`, `<select>`, or content-editable elements via
   the shared `isTypingInInput` helper.