Add updateExisting option to importers & UI

Introduce an updateExisting flag across importers and the Importer UI to control whether existing items should be updated or only new items imported. Changes: added updateExisting to XBVR, StashAPP, Playnite, and Jellyfin config types; added checkboxes in ImporterView (enabled by default) to toggle the behavior; import logic now skips existing items when updateExisting is false and logs/skips appropriately (XBVR, StashAPP, Playnite, Jellyfin). Also: minor Playnite env parsing tweak for port (undefined when not provided) and small logging/cleanup in the Jellyfin album handling.

src/lib/playniteImporter.ts

@@ -7,6 +7,7 @@ export interface PlayniteConfig {
   ip: string;
   apiToken: string;
   port?: number;
+  updateExisting?: boolean;
 }
 
 export interface ImportProgress {
@@ -194,6 +195,15 @@ export async function importFromPlaynite(
       const existingGame = existingMedia.get(game.name);
       const isUpdate = existingGame !== undefined;
 
+      // Skip if updateExisting is false and item already exists
+      if (!config.updateExisting && isUpdate) {
+        logCallback(`⊘ Skipped game: ${game.name} (already exists, updateExisting is false)`);
+        progressCallback({
+          current: i + 1
+        });
+        continue;
+      }
+
       try {
         // Parse release date
         let year = new Date().getFullYear();