feat: show Bitcoin master fingerprint in wallet keys (#3489)

* feat: show Bitcoin master fingerprint in wallet keys

Add the BIP-32 master fingerprint (XFP) to the Bitcoin wallet keys shown
under Settings > Seed & Keys > Keys, labeled "Master fingerprint".

* fix: keep xPub in Keys tab by splitting silent payment keys into a dedicated list

The Keys tab / Silent Payments tab split relied on a hardcoded item index
(`items.sublist(0, 4)` / `sublist(4)`) that assumed the first four items
were always WIF/private key/public key/xPub. Adding the master fingerprint
as the first item pushed xPub into the Silent Payments tab.

Route Bitcoin silent payment keys into their own `silentPaymentItems` list
instead, and render each tab from its list.

lib/src/screens/wallet_keys/wallet_keys_page.dart

@@ -78,7 +78,7 @@ class _WalletKeysPageBodyState extends State<WalletKeysPageBody>
 
     showKeyTab = widget.walletKeysViewModel.items.isNotEmpty;
     showSilentPaymentsTab =
-        widget.walletKeysViewModel.isBitcoin && widget.walletKeysViewModel.items.length > 4;
+        widget.walletKeysViewModel.isBitcoin && widget.walletKeysViewModel.silentPaymentItems.isNotEmpty;
     showLegacySeedTab = widget.walletKeysViewModel.legacySeedSplit.isNotEmpty;
     isLegacySeedOnly = widget.walletKeysViewModel.isLegacySeedOnly;
 
@@ -157,16 +157,12 @@ class _WalletKeysPageBodyState extends State<WalletKeysPageBody>
                 if (showKeyTab)
                   Padding(
                     padding: const EdgeInsets.only(left: 22, right: 22),
-                    child: _buildKeysTab(
-                        context,
-                        showSilentPaymentsTab
-                            ? widget.walletKeysViewModel.items.sublist(0, 4)
-                            : widget.walletKeysViewModel.items),
+                    child: _buildKeysTab(context, widget.walletKeysViewModel.items),
                   ),
                 if (showSilentPaymentsTab)
                   Padding(
                     padding: const EdgeInsets.only(left: 22, right: 22),
-                    child: _buildKeysTab(context, widget.walletKeysViewModel.items.sublist(4)),
+                    child: _buildKeysTab(context, widget.walletKeysViewModel.silentPaymentItems),
                   ),
                 if (showLegacySeedTab)
                   Padding(