Fix redirect source path for foundry docs

[kinderjoypresents]

What: added missing leading / in redirect source
Why: ensures redirect matches consistently

[cursor]

PR Summary

Fixes docs redirect configuration.

• Corrects source for build-on-abstract/smart-contracts/foundry to /build-on-abstract/smart-contracts/foundry, ensuring it redirects to .../foundry/get-started as intended.

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