docs(scrape): the `parsers` option is only documented under Parse

The `parsers` option (and everything under it) is documented only on the [Parse](https://docs.firecrawl.dev/features/parse#pdf-options) page, under a heading called "PDF options". But it is a shared scrape option, and works identically on `/v2/scrape`.

Result: anyone reading the Scrape docs has no way to discover `pages`, `blocks`, `pageMarkers`, `mode`, `maxPages`, or `parsers: []`. The Scrape page never mentions `parsers` at all.

Verified against the live API:

```bash
curl -X POST https://api.firecrawl.dev/v2/scrape \
-H "Authorization: Bearer fc-YOUR-KEY" \
-H 'Content-Type: application/json' \
-d '{"url":"https://example.com/report.pdf","formats":["markdown"],
"parsers":[{"type":"pdf","pages":true,"blocks":true,"pageMarkers":true}]}'
```

returns `pages` and `blocks` alongside `markdown`, exactly as `/v2/parse` does. The JS SDK agrees: `ScrapeOptions.parsers?: Array`, and the response type declares `pages` / `blocks` with the comment "present only when `parsers[].pages` is true".

`maxPages` is the one that costs people money to not know about. On a 184-page PDF:

| request | numPages | creditsUsed |
|---|---|---|
| `parsers: [{type:"pdf", maxPages:1}]` | 1 | 1 |
| `parsers: [{type:"pdf"}]` | 184 | 184 |

Same URL, 184x cost difference, and the option is invisible to a Scrape reader.

### Suggested fix

Add a `parsers` section to the [Scrape](https://docs.firecrawl.dev/features/scrape) page (or a short "Document options" section linking to the Parse reference), so the option is discoverable from the endpoint most people use for PDFs. Renaming the Parse page's "PDF options" to something endpoint-neutral would also help, since it currently reads as parse-only.

Start with the linked Scrape and Parse documentation pages, especially the Parse page's "PDF options" section. Add a discoverable parsers or document-options section to the Scrape page, or link clearly to the shared reference, and make the endpoint-neutral wording reflect pages, blocks, pageMarkers, mode, maxPages, and parsers[]. Verify that a Scrape reader can find these options and understand the maxPages cost impact.

Written by the indexing model from the issue text.