chore: pin tool versions

Author: cinnabarhorse

.nvmrc

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+22.18.0
+

.tool-versions

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+nodejs 22.18.0
+

TOOLCHAIN.md

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+# Toolchain
+
+This repo uses both Foundry (forge) and Hardhat (Node.js) to compile/test/deploy Aavegotchi contracts.
+
+## Node.js
+
+Recommended:
+- `22.18.0` (see `.nvmrc` / `.tool-versions`)
+
+## Foundry
+
+Recommended:
+- Foundry stable (tested with `forge 1.3.5-stable`)
+
+Install:
+- https://book.getfoundry.sh/getting-started/installation
+
+Verify:
+```bash
+forge --version
+```
+
+Notes:
+- `foundry.toml` enables FFI.
+
+## Submodules
+
+This repo uses git submodules (for example `lib/forge-std`). If builds fail due to missing deps:
+
+```bash
+git submodule update --init --recursive
+```
+