perf(frontend): parallelize video thumbs, batch owner-cache writes, minor tweaks

- photos: generate + upload the three video-thumbnail sizes in parallel via
  Promise.allSettled instead of a sequential await loop; previewData is still
  captured before its upload so the local preview survives a failed upload.
- useOwnerCache: resolve the batch, then apply a single reactive assignment
  to `#names` instead of spread-copying the record once per id (fewer copies
  and fewer derive re-runs on large resolves).
- admin: migration status polling slowed from 2s to 5s.
- files store: soft cap (10k) on the per-item selection toggle. Bulk
  "select all" in the views is intentionally left uncapped.

frontend/src/lib/composables/useOwnerCache.svelte.ts

@@ -31,14 +31,16 @@ export class OwnerCache {
 
 	/** Resolve every not-yet-cached id in parallel; nullish ids are skipped. */
 	async resolve(ids: Iterable<string | null | undefined>): Promise<void> {
-		const unique = [...new Set([...ids].filter((id): id is string => !!id))];
-		await Promise.all(
-			unique.map(async (id) => {
-				if (this.#names[id]) return;
-				const name = await this.#resolver(id);
-				this.#names = { ...this.#names, [id]: name };
-			})
+		const pending = [...new Set([...ids].filter((id): id is string => !!id))].filter(
+			(id) => !this.#names[id]
 		);
+		if (pending.length === 0) return;
+		const resolved = await Promise.all(
+			pending.map(async (id) => [id, await this.#resolver(id)] as const)
+		);
+		// One reactive assignment for the whole batch instead of one per id, so a
+		// large resolve doesn't spread-copy the record N times (and re-run derives N times).
+		this.#names = { ...this.#names, ...Object.fromEntries(resolved) };
 	}
 }
 

frontend/src/lib/stores/files.svelte.ts

@@ -96,10 +96,15 @@ class FilesStore {
 		this.selection = new Set();
 	}
 
+	// Soft ceiling so the per-item toggle can't grow the set without bound.
+	// (Bulk "select all" lives in the views and intentionally isn't capped —
+	// silently dropping ids there would break batch delete/move.)
+	static readonly MAX_SELECTION = 10_000;
+
 	toggleSelected(id: string): void {
 		const next = new Set(this.selection);
 		if (next.has(id)) next.delete(id);
-		else next.add(id);
+		else if (next.size < FilesStore.MAX_SELECTION) next.add(id);
 		this.selection = next;
 	}
 }

frontend/src/routes/admin/+page.svelte

@@ -320,7 +320,7 @@
 		try {
 			migration = await getMigration();
 			if (migration.status === 'running') {
-				if (!migrationTimer) migrationTimer = setInterval(loadMigration, 2000);
+				if (!migrationTimer) migrationTimer = setInterval(loadMigration, 5000);
 			} else {
 				stopMigrationPoll();
 			}

frontend/src/routes/photos/+page.svelte

@@ -301,11 +301,16 @@
 				['large', 800, 800]
 			];
 			let previewData = '';
-			for (const [size, w, h] of SIZES) {
-				const blob = await bitmapToBlob(bitmap, w, h);
-				if (size === 'preview') previewData = await blobToDataUrl(blob);
-				await uploadThumbnail(file.id, size, blob).catch(() => {});
-			}
+			// Render the blobs and push all three sizes in parallel; `previewData`
+			// is captured before its upload so the local preview shows even if that
+			// upload fails (allSettled swallows per-size failures, as before).
+			await Promise.allSettled(
+				SIZES.map(async ([size, w, h]) => {
+					const blob = await bitmapToBlob(bitmap, w, h);
+					if (size === 'preview') previewData = await blobToDataUrl(blob);
+					await uploadThumbnail(file.id, size, blob);
+				})
+			);
 			if (previewData) videoThumbs = { ...videoThumbs, [file.id]: previewData };
 		} catch {
 			// Keep the generic play badge on failure.