feat(updater): nightly builds and a stable/nightly update channel (#1608)

* feat(updater): nightly builds and a stable/nightly update channel

Every master push publishes its artifacts as a prerelease of
4gray/iptvnator-nightly instead of the rolling test-master draft, with a
version of <next patch>-nightly.<commit date>.<run number> applied in
every build job. Settings → About gains an Update channel switch;
AppUpdateService re-points electron-updater per check (feed repository,
allowPrerelease, channel name, allowDowngrade reset) and reads release
notes from the repository the requested version belongs to. Channel
switches are forward-only: a nightly build stays until a newer stable
release exists.

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

* fix(updater): compute the nightly version once and keep re-runs safe

Review follow-ups: the nightly version is resolved by a leading job and
handed to every build job, and the patch is bumped only when the base
tag already exists so the release-cut window stays below the imminent
release. A re-run never deletes a published nightly; only a draft left
by a failed run is replaced. Typed update-status literals in the
remaining specs carry the new channel fields.

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

* test(packaging): expect the nightly-version prerequisite in the build workflow graph

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

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

libs/services/src/lib/settings-store.service.ts

@@ -29,6 +29,7 @@ import {
     StreamFormat,
     Theme,
     VideoPlayer,
+    normalizeAppUpdateChannel,
     normalizeEpgOffsetMinutes,
     normalizeDashboardRailsSettings,
     normalizeStartupWindowMode,
@@ -49,6 +50,7 @@ const DEFAULT_SETTINGS: Settings = {
     showDashboard: true,
     startupBehavior: StartupBehavior.FirstView,
     startupWindowMode: 'normal',
+    updateChannel: 'stable',
     showExternalPlaybackBar: true,
     stripCountryPrefix: false,
     theme: Theme.SystemTheme,
@@ -288,6 +290,9 @@ export const SettingsStore = signalStore(
                     startupWindowMode: normalizeStartupWindowMode(
                         store.startupWindowMode?.()
                     ),
+                    updateChannel: normalizeAppUpdateChannel(
+                        store.updateChannel?.()
+                    ),
                     showExternalPlaybackBar:
                         store.showExternalPlaybackBar?.() ??
                         DEFAULT_SETTINGS.showExternalPlaybackBar,