docs: fix broken Flashblocks FAQ anchor links

[devorun]

What changed? Why?

Two pages link into the Flashblocks FAQ using fragments derived from <Accordion> titles:

• eth_call → flashblocks/faq#why-does-eth_call-pending-report-a-block-number-several-blocks-behind-tip
• Flashblocks API overview → flashblocks/faq#can-the-flashblock-index-exceed-10-is-that-a-bug

Accordion titles are not headings, so no anchor is generated for them and neither fragment resolves. Both links currently land at the top of the FAQ instead of the relevant answer.

This repoints them to the headings of the sections that contain those accordions:

• the eth_call "pending" answer lives under ## RPC → #rpc
• the Flashblock index answer lives under ## WebSocket → #websocket

Notes to reviewers

These are the only two cross-references in the docs that target accordion titles rather than headings; every other anchor link points at a real heading. Section-level anchors are the closest working targets without adding explicit anchors to the FAQ. Only the two linking pages are touched — faq.mdx itself is unchanged.

How has it been tested?

Checked that flashblocks/faq.mdx contains no headings matching either fragment, and confirmed the two answers sit under the ## RPC and ## WebSocket headings whose anchors are #rpc and #websocket.

[cb-heimdall]

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