docs: fix incorrect link in use-for-fees guide

[alelpoan]

Fix a link that points to the wrong page in the use-for-fees guide.

The text says "See the [Create a Stablecoin] guide for instructions on minting fee AMM liquidity.", but that page only covers token creation, it contains no instructions on minting fee AMM liquidity.
The Managing Fee Liquidity page is the correct target, as it covers adding liquidity to the fee pool, LP tokens, and first liquidity provider flow.

Changes:

• guide/issuance/use-for-fees.md: [Create a Stablecoin](/guide/issuance/create-a-stablecoin) → [Managing Fee Liquidity](/guide/stablecoin-dex/managing-fee-liquidity)

Test plan
Documentation-only change; no code paths affected.

[vercel]

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