fix(web): satisfy contracts-ready lint and dedup the stable-file read

Rescope nothing new: drop the needless async from the inherited readRaw
default (reject explicitly on abort), fix the void arrow shorthand in
downloadBlob, and share one revision-stable file-read loop between readRaw
and readPrefix in the JSONL backend.

packages/client/ui-trajectory/src/client/export-log.ts

@@ -38,5 +38,5 @@ export function downloadBlob(blob: Blob, filename: string): void {
   anchor.download = filename
   anchor.click()
   // Revoke one tick later: some browsers read the blob URL after click().
-  setTimeout(() => URL.revokeObjectURL(url), 0)
+  setTimeout(() => { URL.revokeObjectURL(url) }, 0)
 }