feat(portals): carry VOD source pins through playlist backup

The new pins table was invisible to backup: exporting a playlist and
re-importing it on a new machine silently dropped every "main source" choice,
with nothing in the archive to say the choice had ever been made.

Pins now ride along under the playlist they point AT — carrying them anywhere
else would restore a preference for a portal the archive never contained.
`matchKey` names the film rather than the portal, so it survives untouched and
only the playlist id is remapped to the imported copy.

`sourcePins` is the one optional collection in the Xtream user state: archives
written before multi-source existed simply do not have it, so its absence is
age rather than damage. Only a wrong type is rejected, and pins without a
usable match key or content id are dropped, since writing one would occupy the
unique key of a film it does not describe.

Adds `DB_LIST_VOD_SOURCE_PINS` through the usual six seams (operation, worker
case, event, preload, bridge contract, service).

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

libs/shared/interfaces/src/lib/electron-api.interface.ts

@@ -880,6 +880,8 @@ export interface ElectronBridgeApi {
     }) => Promise<VodSourceCandidateRow[]>;
     /** Per-movie pinned source; keys are passed most-trusted first */
     dbGetVodSourcePin: (matchKeys: string[]) => Promise<VodSourcePin | null>;
+    /** Every pin pointing at this playlist — used by playlist backup. */
+    dbListVodSourcePins: (playlistId: string) => Promise<VodSourcePin[]>;
     dbSetVodSourcePin: (pin: VodSourcePin) => Promise<ElectronBridgeResult>;
     dbClearVodSourcePin: (
         matchKeys: string[]