docs: add manual derivation type selection UX guidelines

- Add alternative implementation for explicit user selection during onboarding
- Include code example for manual derivation type selection UI
- Document benefits and use cases for manual vs automatic selection
- Address scenarios where users have used multiple derivation types
- Provide clear guidance for multi-wallet applications

Author: rhyslbw

packages/hardware-trezor/MASTER_KEY_GENERATION.md

@@ -94,6 +94,8 @@ const keyAgent = await TrezorKeyAgent.createWithDevice({
 
 ## Discovery & UX Guidelines
 
+### Automatic Discovery Pattern
+
 When pairing a Trezor device, follow this discovery pattern to find existing accounts:
 
 1. **Try ICARUS first** - Most common for software wallets
@@ -102,6 +104,43 @@ When pairing a Trezor device, follow this discovery pattern to find existing acc
 
 This is why many wallet UIs show a "Derivation type override" dropdown - to help users discover their existing accounts.
 
+### Manual Selection During Onboarding
+
+For applications that prefer explicit user control, consider exposing derivation type selection during the onboarding process:
+
+```typescript
+// Example onboarding flow
+const derivationTypeOptions = [
+  { value: 'ICARUS', label: 'Software Wallet', description: 'Most common for wallets created with software applications' },
+  { value: 'ICARUS_TREZOR', label: 'Trezor Default', description: 'Trezor\'s internal default (24-word mnemonic compatible)' },
+  { value: 'LEDGER', label: 'Ledger Hardware Wallet', description: 'For wallets originally created on Ledger devices' }
+];
+
+// Let user select during onboarding
+const selectedDerivationType = await showDerivationTypeSelection(derivationTypeOptions);
+
+const keyAgent = await TrezorKeyAgent.createWithDevice({
+  chainId: Cardano.ChainIds.Mainnet,
+  trezorConfig: {
+    communicationType: 'web',
+    manifest: { email: '[email protected]', appUrl: 'https://myapp.com' },
+    derivationType: selectedDerivationType
+  }
+}, dependencies);
+```
+
+**Benefits of Manual Selection:**
+- **User Control**: Users explicitly choose their derivation type
+- **Multi-Wallet Support**: Users can create multiple wallets with different derivation types
+- **Transparency**: Clear understanding of which derivation type is being used
+- **No Guessing**: Eliminates the need for automatic discovery patterns
+
+**When to Use Manual Selection:**
+- Applications that prioritize user control and transparency
+- Multi-wallet applications where users might have accounts with different derivation types
+- Enterprise applications where explicit configuration is preferred
+- When users have used multiple wallet types and need to access different accounts
+
 ## Implementation Details
 
 When a non-default derivation type is specified, the SDK sets the appropriate `derivationType` in the `cardanoSignTransaction` call. For the default type, no `derivationType` is sent to Trezor.
@@ -119,8 +158,3 @@ Existing wallets without a `derivationType` configuration will continue to work
 - **[Trezor Forum](https://forum.trezor.io/t/cardano-ada-transaction-signing-error/10466)**: Community discussion on derivation types
 - **[Cardano Stack Exchange](https://cardano.stackexchange.com/questions/5977/how-does-ledger-generate-the-public-keys)**: Ledger key generation details
 - **[Cardano Foundation](https://cardano-foundation.github.io/cardano-wallet/concepts/master-key-generation)**: Master key generation background
-
-## Notes
-
-- **Device Compatibility**: Ensure your Trezor device firmware supports the chosen derivation type
-- **Discovery**: Use the discovery pattern (ICARUS → ICARUS_TREZOR → LEDGER) to find existing accounts