docs(intake): correct a false claim about cut-out durability (#281)

The module comment on backgroundRemoval.ts said "The original file stays on disk and so does every cut-out ever made." The original half is true and load-bearing; the cut-out half is not. cutoutPathFor is deterministic, so a photo that is restored and then cut out again overwrites the previous cut-out at the same path. Harmless — no original is ever touched — but the comment overstated what the module guarantees. Corrected it to say what is actually true.

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

backend/src/intake/backgroundRemoval.ts

@@ -12,10 +12,14 @@ import { isRembgConfigured, removeBackground } from './rembgClient';
  * undoable the same way. A near-copy that drifted would mean a photo the
  * Restore button could not restore.
  *
- * Nothing here deletes anything. The original file stays on disk and so does
- * every cut-out ever made, because the submitter's photos are often the only
- * copy of an item no longer in their hands — the same rule Discard follows in
- * the review queue.
+ * Nothing here deletes anything. The original file always stays on disk,
+ * because the submitter's photos are often the only copy of an item no longer
+ * in their hands — the same rule Discard follows in the review queue. A
+ * cut-out is not as durable: `cutoutPathFor` is deterministic, so a photo that
+ * is restored and then cut out again writes over the previous cut-out at the
+ * same path. That is harmless — no original is ever touched — but it means
+ * "every cut-out ever made" is not actually true, so this comment used to
+ * overstate it.
  */
 
 interface ImageRow {