docs(scrape): document the PDF/document size limit and whether it can be raised

[RichardBray]

Parse documents a 50MB per-request cap. Scrape documents no size limit at all, and the two behave very differently when you cross one.

What I observed

Same 63MB PDF (a 60MB journal issue), both endpoints:

endpoint	result	time
/v2/parse	Uploaded file exceeds maximum size of 50MB	9s
/v2/scrape	SCRAPE_TIMEOUT	4m40s (at timeout: 280000)

A 26MB PDF through /v2/scrape parsed in 1.9s, so this is not "big PDFs are slow". I also ruled out a slow origin: curl pulled the full 63MB in 4.5s.

So scrape appears to have a size ceiling in the same neighborhood, but instead of a size error you get a timeout after several minutes. In a pipeline that reads as a flaky source, so the natural response is to retry, which costs more time and (per the billing docs, credits are charged whenever infrastructure processes a request) possibly more credits.

Requests

1. Document scrape's document size limit. Even "documents above ~50MB may not complete" would let people plan.
2. Say whether it can be raised. My understanding is that this ceiling is account-level rather than a request parameter; there is no setting for it in the dashboard (Overview / Activity Logs / Usage / API Keys / Settings). If raising it is possible, the docs should say who to ask; if not, it should say that too.
3. Consider a clearer failure than SCRAPE_TIMEOUT. An explicit "document exceeds size limit" would be far more actionable. Filing here since it is a docs repo, happy to move that third point to the main repo if preferred.

Why it matters

The Parse page tells you the limit up front and fails fast and cheap. Scrape is the endpoint most people point at PDFs, and it currently fails slow and silent.