Fix TextDecoder constructor: remove invalid stream option

The stream option belongs on decode() calls, not the constructor.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: samsel

src/lib/mbox-parser.ts

@@ -67,7 +67,7 @@ export async function parseMboxStream(
   onEmail: (raw: ArrayBuffer) => Promise<void>,
 ): Promise<number> {
   const reader = stream.getReader()
-  const decoder = new TextDecoder('utf-8', { stream: true })
+  const decoder = new TextDecoder('utf-8')
   let emailCount = 0
 
   // Accumulates the current mbox segment (one "From ..." block)