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

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

step-02-device-app-lib/README.md

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+# Step 2 — Device app lib
+
+- **EVM/Chain 138:** Use existing `@ledgerhq/hw-app-eth`; no new device app lib. Ensure `chainId: 138` in transaction building/signing.
+- **app-ethereum (C):** If upstream Ledger app-ethereum does not list Chain 138, add the line from `network-entry-chain138.c` to `src/network.c`. Our fork already has it at `pr-workspace/app-ethereum/src/network.c` line 42.
+- **Icons:** If Ledger requires a network icon, use their icon process (see Device App Kit docs). Chain 138 can share the generic Ethereum-style icon until a custom one is added.

step-02-device-app-lib/hw-app-eth-usage.ts

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+/**
+ * Step 2 — Device app lib (JS bindings)
+ * For EVM/Chain 138 we use existing @ledgerhq/hw-app-eth. No new package needed.
+ * Ensure chainId 138 is passed when building/signing transactions.
+ *
+ * Example usage in coin-module or live-common (signer/bridge):
+ */
+
+import Eth from "@ledgerhq/hw-app-eth";
+
+const CHAIN_ID_138 = 138;
+
+// When getting address (path is BIP44 EVM: 44'/60'/0'/0/0)
+async function getAddress(
+  transport: { send: (cla: number, ins: number, p1: number, p2: number, data?: Buffer) => Promise<Buffer> },
+  path: string,
+  display?: boolean
+) {
+  const eth = new Eth(transport);
+  const result = await eth.getAddress(path, display ?? false);
+  return { address: result.address, publicKey: result.publicKey, path };
+}
+
+// When signing a transaction, the serialized tx must include chainId 138 (EIP-155)
+// so the device shows "Defi Oracle Meta" and signs correctly.
+function buildTxWithChainId(tx: { chainId?: number; [k: string]: unknown }) {
+  return { ...tx, chainId: tx.chainId ?? CHAIN_ID_138 };
+}
+
+export { getAddress, buildTxWithChainId, CHAIN_ID_138 };

step-02-device-app-lib/network-entry-chain138.c

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+/**
+ * Step 2 — Device app lib (app-ethereum network entry)
+ * Target: LedgerHQ/app-ethereum src/network.c
+ *
+ * Our fork already has Chain 138 at line 42. This snippet is for upstream Ledger
+ * app-ethereum if they don't yet list Chain 138. Add one line to NETWORK_MAPPING[].
+ *
+ * Format: {.chain_id = 138, .name = "Defi Oracle Meta", .ticker = "ETH"},
+ */
+
+/* Insert in src/network.c inside NETWORK_MAPPING[], e.g. after Polygon (137): */
+{.chain_id = 138, .name = "Defi Oracle Meta", .ticker = "ETH"},