feat: add microloans stack type with MiniPay flows

[nomoregas]

Adds a Microloans stack type for the step-up microloans contract (BreadchainCoop/saving-circles#198): a lender offers a zero-interest loan to one borrower and escrows a grant that unlocks once the loan is repaid. Everything is behind the new microloans feature flag.

What's in it

• /new/microloan: offer a loan (approve + create). Optional borrower address and a plain-language agreement whose hash becomes termsHash.
• /microloans/[id]:
  • Borrower: accept (when there's an agreement, the pasted text must match before Accept enables) and repay any amount, with an "All" shortcut.
  • Anyone: release the grant once the loan is repaid.
  • Lender: set the borrower, cancel, extend the deadline, reclaim the grant when overdue, and collect repayments.
• Microloans list on the account page.
• Low-balance hint that links to MiniPay Add Cash.
• waitForTxReceipt now returns the receipt, so create can read LoanCreated. Existing callers ignore the return value.

Chain state only for now: no Supabase metadata or invite links.

Testnet deployment

Microloans is deployed on Celo Sepolia at 0xbB1428678354c1694188066Bf5C04BcfaD5C9653, with test USDC (0x01C5C0122039549AD1493B8220cABEdD739BC44E) allowed.

To make the deploy preview usable (needs a maintainer)

Add these to the deploy-preview environment in Netlify. It must be a Celo Sepolia environment (NEXT_PUBLIC_CHAIN_ID=11142220, USDC deposit token with 6 decimals):

• NEXT_PUBLIC_MICROLOANS_CONTRACT_ADDRESS=0xbB1428678354c1694188066Bf5C04BcfaD5C9653
• "microloans":{"enabled":true} added to NEXT_PUBLIC_FEATURES

Testing

• pnpm lint, tsc, and prettier --check . pass.
• Ran the MiniPay provider stack against a local anvil chain with a window.ethereum.isMiniPay shim, at a 375px viewport. Exercised these flows and checked the on-chain results:
  • create (approve + create, redirect)
  • set borrower
  • accept (with mismatched and matching agreement text)
  • repay in full
  • release grant
  • collect
  • the account list
• Not yet exercised: cancel, extend, and reclaim (they need an expired or overdue loan), plus a real MiniPay device.

[netlify]

👷 Deploy request for app-stacks pending review.

Visit the deploys page to approve it

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🔨 Latest commit	cac1555