Nuke buy providers + flip node defaults from Cake to community

Buy providers (Robinhood Connect, DFX, Onramper, MoonPay, Kryptonim, Meld):
- lib/entities/provider_types.dart: getAvailable{Buy,Sell}ProviderTypes()
  both return [] now. Each provider requires a formal partner contract
  with revenue-share — no free integrations exist. Re-add to the list
  once Such Software has registered the partner relationship per provider.
  Buy/Sell UI surfaces (cards_view.dart's onramp button -> Routes.buySellPage)
  still render but the provider list is empty, so the screen shows nothing.
- lib/view_model/support_view_model.dart: removed the third-party support
  LinkListItem entries for the dead buy providers. Kept the swap-provider
  support links (ChangeNow, SideShift, SimpleSwap, Exolix, SwapTrade,
  Trocador) — Trocador is still active and the others are useful for
  legacy users who created swaps before the trim.

Default node flip (per user request — 'someone else top choice, Cake nodes
stay in the list of others'):
- xmr-node.cakewallet.com:18081  -> node.sethforprivacy.com:443
- electrum.cakewallet.com:50002  -> electrum.blockstream.info:50002
- ltc-electrum.cakewallet.com:50002 -> electrum-ltc.bysh.me:50002
- btc-electrum.cakewallet.com:50002 -> electrum.blockstream.info:50002
Cake's nodes remain in the augmented lists (see asset/*_node_list.yml).
Silent-payments Electrs (electrs.cakewallet.com) + zcash default URI
unchanged — no good free alternative for silent payments, and zcash is
removed anyway.

lib/entities/default_settings_migration.dart

@@ -30,14 +30,14 @@ import 'package:shared_preferences/shared_preferences.dart';
 import 'package:cw_core/cake_hive.dart';
 import 'package:cw_core/erc20_token.dart';
 
-const newCakeWalletMoneroUri = 'xmr-node.cakewallet.com:18081';
+const newCakeWalletMoneroUri = 'node.sethforprivacy.com:443';  // Hash Wallet: default flipped to community node
-const cakeWalletBitcoinElectrumUri = 'electrum.cakewallet.com:50002';
+const cakeWalletBitcoinElectrumUri = 'electrum.blockstream.info:50002';  // Hash Wallet: default flipped to Blockstream
 const cakeWalletSilentPaymentsElectrsUri = 'electrs.cakewallet.com:50001';
 const publicBitcoinTestnetElectrumAddress = 'electrs.cakewallet.com';
 const publicBitcoinTestnetElectrumPort = '50002';
 const publicBitcoinTestnetElectrumUri =
     '$publicBitcoinTestnetElectrumAddress:$publicBitcoinTestnetElectrumPort';
-const cakeWalletLitecoinElectrumUri = 'ltc-electrum.cakewallet.com:50002';
+const cakeWalletLitecoinElectrumUri = 'electrum-ltc.bysh.me:50002';  // Hash Wallet: default flipped to bysh.me community node
 const havenDefaultNodeUri = 'nodes.havenprotocol.org:443';
 const ethereumDefaultNodeUri = 'ethereum-rpc.publicnode.com';
 const polygonDefaultNodeUri = 'polygon-bor-rpc.publicnode.com';
@@ -46,7 +46,7 @@ const nanoDefaultNodeUri = 'rpc.nano.to';
 const nanoDefaultPowNodeUri = 'rpc.nano.to';
 const solanaDefaultNodeUri = 'solana-mainnet.core.chainstack.com';
 const tronDefaultNodeUri = 'api.trongrid.io';
-const newCakeWalletBitcoinUri = 'btc-electrum.cakewallet.com:50002';
+const newCakeWalletBitcoinUri = 'electrum.blockstream.info:50002';  // Hash Wallet: default flipped to Blockstream
 const wowneroDefaultNodeUri = 'node3.monerodevs.org:34568';
 const zanoDefaultNodeUri = '37.27.100.59:10500';
 const moneroWorldNodeUri = '.moneroworld.com';

lib/entities/provider_types.dart

@@ -46,21 +46,13 @@ extension ProviderTypeName on ProviderType {
 }
 
 class ProvidersHelper {
-  static List<ProviderType> getAvailableBuyProviderTypes() => [
+  // Hash Wallet: all buy/sell providers (Robinhood Connect, DFX, Onramper,
-    ProviderType.robinhood,
+  // MoonPay, Kryptonim, Meld) gutted. Each requires a formal partner
-    ProviderType.dfx,
+  // agreement with a revenue-share contract — no free integrations exist.
-    ProviderType.onramper,
+  // Re-add providers here once Such Software has registered the affiliate
-    ProviderType.moonpay,
+  // relationship for that provider.
-    ProviderType.kriptonim
+  static List<ProviderType> getAvailableBuyProviderTypes() => [];
-  ];
+  static List<ProviderType> getAvailableSellProviderTypes() => [];
-
-  static List<ProviderType> getAvailableSellProviderTypes() => [
-    // ProviderType.robinhood, // ToDo: (Konsti) Enable once fixed in Exchange Helper, but still waiting for new Docs
-    ProviderType.dfx,
-    ProviderType.onramper,
-    ProviderType.moonpay,
-    ProviderType.kriptonim
-  ];
 
   static BuyProvider getProviderByType(ProviderType type) {
     switch (type) {

lib/view_model/support_view_model.dart

@@ -63,37 +63,7 @@ abstract class SupportViewModelBase with Store {
               icon: 'assets/images/trocador.png',
               linkTitle: 'mail@trocador.app',
               link: 'mailto:mail@trocador.app'),
-          LinkListItem(
-              title: 'Onramper',
-              icon: 'assets/images/onramper_dark.png',
-              lightIcon: 'assets/images/onramper_light.png',
-              linkTitle: 'View exchanges',
-              link: 'https://onramper.com/'),
-          LinkListItem(
-              title: 'DFX',
-              icon: 'assets/images/dfx_dark.png',
-              lightIcon: 'assets/images/dfx_light.png',
-              linkTitle: 'support@dfx.swiss',
-              link: 'mailto:support@dfx.swiss'),
           if (!isMoneroOnly) ...[
-            LinkListItem(
-                title: 'MoonPay',
-                icon: 'assets/images/moonpay.png',
-                linkTitle: S.current.submit_request,
-                link: 'https://support.moonpay.com/hc/en-gb/requests/new'),
-            LinkListItem(
-                title: 'Robinhood Connect',
-                icon: 'assets/images/robinhood_dark.png',
-                lightIcon: 'assets/images/robinhood_light.png',
-                linkTitle: S.current.submit_request,
-                link: 'https://robinhood.com/contact')
-          ],
-          LinkListItem(
-              title: 'Kryptonim',
-              icon: 'assets/images/kryptonim_dark.png',
-              lightIcon: 'assets/images/kryptonim_light.png',
-              linkTitle: 'contact@support.kryptonim.com',
-              link: 'mailto:contact@support.kryptonim.com'),
         ];
 
   final docsUrl = 'https://github.com/Such-Software/hash-wallet';