chore: sync submodule state (parent ref update)

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docs/nft/GRU_FORMULAS_NFT.md

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+# GRU Formulas NFT
+
+**Contract**: `contracts/nft/GRUFormulasNFT.sol`  
+**Standard**: ERC-721
+
+---
+
+## Overview
+
+The GRU Formulas NFT mints up to three token types, each depicting a GRU-related monetary formula as an on-chain SVG graphic.
+
+## Token ID Mapping
+
+| Token ID | Formula        | Name / Description |
+|----------|----------------|--------------------|
+| **0**    | Money Supply   | GRU monetary layers: **1 M00 = 5 M0 = 25 M1** (base M00, collateral M0, credit M1). See `GRUConstants.sol`. |
+| **1**    | Money Velocity | Equation of exchange: **M × V = P × Y** (money supply × velocity = price level × output). |
+| **2**    | Money Multiplier | **m = Reserve / Supply = 1.0** — no fractional reserve; enforced in ComplianceGuard and ISO4217W tokens. |
+
+## Minting
+
+- Only addresses with `MINTER_ROLE` can mint.
+- `mint(to, tokenId)` with `tokenId` 0, 1, or 2.
+- There are exactly three NFTs: tokenId 0, 1, and 2 (one per formula). Each tokenId can be minted once; the recipient receives that formula’s graphic.
+
+## Metadata
+
+- `tokenURI(tokenId)` returns a data URI: `data:application/json;base64,<base64(JSON)>`.
+- The JSON includes `name`, `description`, and `image`.
+- The `image` field is a data URI with an on-chain SVG: `data:image/svg+xml;base64,<base64(SVG)>`.
+- No off-chain or IPFS dependency; all graphics are on-chain.
+
+## Deployment
+
+Deploy with an admin address (receives `DEFAULT_ADMIN_ROLE` and `MINTER_ROLE`). Grant `MINTER_ROLE` to any additional minters as needed.
+
+```bash
+forge create contracts/nft/GRUFormulasNFT.sol:GRUFormulasNFT --constructor-args <ADMIN_ADDRESS> --rpc-url $RPC_URL --private-key $PRIVATE_KEY
+```
+
+## References
+
+- GRU layers: `contracts/vault/libraries/GRUConstants.sol`
+- Money multiplier validation: `contracts/iso4217w/ComplianceGuard.sol`, `docs/OPERATIONS_RUNBOOK.md`