Add full Chain 138 integration: 8 steps, chain spec, app-ethereum config, docs

Co-authored-by: Cursor <cursoragent@cursor.com>

step-07-wallet-api/walletApiAdapter.chain138.ts

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+/**
+ * Step 7 — Wallet API: Ledger Wallet adapter (WalletAPI tx <-> LL tx)
+ * Target: ledger-live libs/ledger-live-common/src/families/ethereum/walletApiAdapter.ts
+ *
+ * If Chain 138 is exposed via Wallet API, ensure the adapter maps WalletAPI
+ * Ethereum transaction (with chainId 138) to Ledger Wallet Ethereum transaction.
+ * Add to the generated walletApiAdapter dispatch (via sync-families-dispatch script).
+ */
+
+/*
+// Example: in libs/ledger-live-common/src/families/ethereum/walletApiAdapter.ts
+export function fromWalletAPITransaction(
+  walletApiTx: WalletAPIEthereumTransaction
+): EthereumTransaction {
+  return {
+    ...walletApiTx,
+    chainId: walletApiTx.chainId ?? 138,
+  };
+}
+
+export function toWalletAPITransaction(
+  llTx: EthereumTransaction
+): WalletAPIEthereumTransaction {
+  return {
+    ...llTx,
+    chainId: llTx.chainId,
+  };
+}
+*/
+
+export const ADAPTER_NOTE =
+  "Extend ethereum walletApiAdapter to handle chainId 138; register in sync-families-dispatch so generated walletApiAdapter.ts includes it.";