feat(portals): find the same movie in your other playlists

A movie that exists in several imported Xtream playlists now shows a
"Sources N" chip on its detail page and in the player. Switching playlist
mid-film keeps the timecode, a preferred source can be pinned per movie, and
a failed stream offers the alternatives instead of a dead end.

The governing rule is that a guess is never presented as a fact. Every
metadata value carries where it came from — `api` (the provider said so),
`parsed` (inferred from the title) or `probe` (we contacted the stream).
Facts render as plain tags, guesses are prefixed `~` in a warning colour, and
an unknown value renders no tag at all plus a "check" affordance. Ranking and
failover read through `factualOnly()`, so a filename claiming 4K is
structurally unable to outrank a source that was actually reached. A probe
that could not complete reports "unknown", never "unavailable".

Scope is deliberately narrow: Xtream to Xtream, movies only, Electron only.
Stalker never reaches the `content` table and M3U is a JSON blob whose search
forces live content; both are additive later, since the candidate type
already carries all three portal kinds. In the PWA every entry point is gated
off and the chip renders nothing.

Auto-failover is opt-in and off by default. Each source is tried at most once
per session, so it terminates structurally, and the switch is never silent —
the toast names the new playlist, offers an undo, and warns that the dub may
differ only when both sides state an audio track as fact.

Notable details:
- Playlist names are routinely the pasted URL, credentials included. They are
  never rendered raw; a short host-only label is derived instead.
- Quality is derived from pixel width, not height: a 2.39:1 1080p master is
  1920x800, and bucketing that by height would publish "720p" as a fact.
- Switching is a single `inlinePlayback.set()` so the player and engine
  survive and re-seek; the carried position is read before the 15s
  persistence throttle so it does not rewind.
- Sources from one playlist collapse into a group, since the same film often
  appears there several times under different stream ids.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

libs/ui/playback/src/lib/web-player-view/web-player-view.component.html

@@ -127,6 +127,36 @@
                 </div>
             }
 
+            @if (alternativeSources().length > 0) {
+                <div
+                    class="web-player-diagnostic__alternatives"
+                    data-test-id="playback-alternative-sources"
+                >
+                    <h3 class="web-player-diagnostic__alternatives-title">
+                        {{
+                            'PORTALS.MULTI_SOURCE.TRY_ANOTHER_SOURCE'
+                                | translate
+                        }}
+                    </h3>
+                    @for (source of visibleAlternatives(); track source.id) {
+                        <app-vod-source-row
+                            [source]="source"
+                            [showPin]="false"
+                            (playRequested)="alternativeSourceRequested.emit($event)"
+                        />
+                    }
+                    @if (hiddenAlternativeCount() > 0) {
+                        <p class="web-player-diagnostic__alternatives-more">
+                            {{
+                                'PORTALS.MULTI_SOURCE.MORE_SOURCES'
+                                    | translate
+                                        : { count: hiddenAlternativeCount() }
+                            }}
+                        </p>
+                    }
+                </div>
+            }
+
             @if (canShowExternalFallbackActions()) {
                 <div
                     class="web-player-diagnostic__player-actions"