improve binary file detection: content sniffing + jsonl support

Files like .jsonl that mime-types doesn't know fell through to
application/octet-stream and rendered as "Unsupported binary file" in
the viewer. Replace istextorbinary with isbinaryfile for content-based
detection, and use mime-types for name-based classification with a
textual application/* allowlist.

The streaming transformer now defers classification when the name is
inconclusive and sniffs the first chunk before emitting "transform",
so route.ts and AnonymizedFile.ts get a content-aware Content-Type.
Whitelists .jsonl and .ndjson to short-circuit dataset files.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/config.ts

@@ -69,6 +69,8 @@ const config: Config = {
     "out",
     "sol",
     "in",
+    "jsonl",
+    "ndjson",
   ],
   STORAGE: "filesystem",
   STREAMER_ENTRYPOINT: null,