docs: fix broken DA Footprint anchor link on Jovian upgrade page

[devorun]

What changed? Why?

On the Jovian upgrade overview, the DA Footprint Limit link points to jovian/exec-engine#da-footprint-limit, but the target heading on that page is ## DA Footprint Block Limit, whose generated anchor is #da-footprint-block-limit. The current link is missing block, so it does not resolve to the section.

This updates the fragment to #da-footprint-block-limit to match the actual heading.

Notes to reviewers

Single-line fragment fix in docs/base-chain/specs/upgrades/jovian/overview.mdx. The target heading ## DA Footprint Block Limit is in docs/base-chain/specs/upgrades/jovian/exec-engine.mdx. The sibling links in the same list (#minimum-base-fee, #operator-fee) already resolve correctly.

How has it been tested?

Confirmed the target page has no #da-footprint-limit heading and that ## DA Footprint Block Limit (anchor #da-footprint-block-limit) is the intended section.

[cb-heimdall]

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