refactor(web): consolidate asset operations in PhotostreamManager base class

Moves common asset operation methods (upsertAssets, removeAssets, 
updateAssetOperation) from TimelineManager into PhotostreamManager 
base class, making them available to all photostream implementations. 
Updates all consuming components to use the more accurate 'upsertAssets' 
naming instead of separate 'addAssets' and 'updateAssets' methods.

- Move asset operation methods to PhotostreamManager base class
- Replace addAssets/updateAssets calls with unified upsertAssets method
- Update type imports to use PhotostreamManager instead of TimelineManager
- Remove operations-support.svelte.ts (functionality moved to base class)
- Add abstract upsertAssetIntoSegment method for subclass customization

web/src/lib/managers/photostream-manager/PhotostreamSegment.svelte.ts

@@ -4,7 +4,7 @@ import { t } from 'svelte-i18n';
 import { get } from 'svelte/store';
 
 import type { PhotostreamManager } from '$lib/managers/photostream-manager/PhotostreamManager.svelte';
-import type { TimelineAsset } from '$lib/managers/timeline-manager/types';
+import type { AssetOperation, MoveAsset, TimelineAsset } from '$lib/managers/timeline-manager/types';
 import type { ViewerAsset } from '$lib/managers/timeline-manager/viewer-asset.svelte';
 
 export type SegmentIdentifier = {
@@ -147,4 +147,46 @@ export abstract class PhotostreamSegment {
   }
 
   abstract findAssetAbsolutePosition(assetId: string): number;
+
+  runAssetOperation(ids: Set<string>, operation: AssetOperation) {
+    if (ids.size === 0) {
+      return {
+        moveAssets: [] as MoveAsset[],
+        processedIds: new Set<string>(),
+        unprocessedIds: ids,
+        changedGeometry: false,
+      };
+    }
+    const unprocessedIds = new Set<string>(ids);
+    const processedIds = new Set<string>();
+    const moveAssets: MoveAsset[] = [];
+    let changedGeometry = false;
+    for (const assetId of unprocessedIds) {
+      const index = this.viewerAssets.findIndex((viewAsset) => viewAsset.id == assetId);
+      if (index === -1) {
+        continue;
+      }
+
+      const asset = this.viewerAssets[index].asset!;
+      const oldTime = { ...asset.localDateTime };
+      const opResult = operation(asset);
+      let remove = false;
+      if (opResult) {
+        remove = (opResult as { remove: boolean }).remove ?? false;
+      }
+      const newTime = asset.localDateTime;
+      if (oldTime.year !== newTime.year || oldTime.month !== newTime.month || oldTime.day !== newTime.day) {
+        const { year, month, day } = newTime;
+        remove = true;
+        moveAssets.push({ asset, date: { year, month, day } });
+      }
+      unprocessedIds.delete(assetId);
+      processedIds.add(assetId);
+      if (remove || this.timelineManager.isExcluded(asset)) {
+        this.viewerAssets.splice(index, 1);
+        changedGeometry = true;
+      }
+    }
+    return { moveAssets, processedIds, unprocessedIds, changedGeometry };
+  }
 }