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

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

step-07-wallet-api/validation.ethereum-chain138.ts

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+/**
+ * Step 7 — Wallet API: validation (Zod) for Ethereum family with chainId 138
+ * Target: ledger-live wallet-api packages/core/src/families/ethereum/validation.ts
+ * (If Ledger adds Chain 138 to Ethereum family, ensure chainId 138 is allowed in schema.)
+ *
+ * Example: extend schemaRawEthereumTransaction to allow chainId 138.
+ */
+
+import { z } from "zod";
+
+const CHAIN_ID_138 = 138;
+
+export const schemaRawEthereumTransaction = z.object({
+  family: z.literal("ethereum"),
+  amount: z.string(),
+  recipient: z.string(),
+  gasPrice: z.string().optional(),
+  maxFeePerGas: z.string().optional(),
+  maxPriorityFeePerGas: z.string().optional(),
+  gasLimit: z.string().optional(),
+  data: z.string().optional(),
+  nonce: z.number().optional(),
+  chainId: z.number().refine((id) => id === 1 || id === CHAIN_ID_138, {
+    message: "chainId must be 1 (Ethereum) or 138 (Defi Oracle Meta Mainnet)",
+  }),
+});
+
+export type RawEthereumTransaction = z.infer<typeof schemaRawEthereumTransaction>;