fix: replace broken bridge-token link with Optimism standard bridge docs

[ygd58]

Problem

The link Bridging an L1 Token to Base in bridges.mdx points to a page that does not exist, causing a 404 error reported in #1159.

A redirect exists in docs.json pointing this path to /base-chain/network-information/bridges (the same page), which creates a self-referencing loop.

Fix

Replaced the broken internal link with the official Optimism standard bridge documentation at https://docs.optimism.io/builders/app-developers/bridging/standard-bridge, which covers the exact topic (deploying ERC-20 tokens on Base using standard bridge contracts).

Closes #1159

[cb-heimdall]

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