Skip zcash node loading and migration step 55 (chain removed)

The zcash chain was removed (cw_zcash deleted, assets/zcash_node_list.yml
deleted), but two places still tried to load it at runtime:

1. lib/entities/node_list.dart's resetToDefault() unconditionally called
   loadDefaultNodes(WalletType.zcash) which tried to read the deleted YAML.
2. lib/entities/default_settings_migration.dart migration step 55 called
   addWalletNodeList(type: WalletType.zcash) + _changeDefaultNode for zcash,
   same failure.

Both surfaced as a 'Unable to load asset: assets/zcash_node_list.yml' error
popup on every fresh wallet creation. Removing both call sites; migration
step 55 becomes a no-op (existing wallets advance through it without effect).

Also includes the new SVG variants added to assets/images/hash_wallet/:
03/04/05_*_dark.svg, 09_mark_outline.svg, 10_wordmark_only.svg,
11_vertical_lockup.svg, 12_notification_mono.svg — fills out the brand
kit with dark-theme wordmarks plus tiny/outline/wordmark-only/vertical/
notification variants for cases the existing set didn't cover.

lib/entities/default_settings_migration.dart

@@ -563,13 +563,10 @@ Future<void> defaultSettingsMigration(
           await _backupWowneroSeeds(havenSeedStore);
           break;
         case 55:
-          await addWalletNodeList(nodes: nodes, type: WalletType.zcash);
-          await _changeDefaultNode(
-            nodes: nodes,
-            sharedPreferences: sharedPreferences,
-            type: WalletType.zcash,
-            currentNodePreferenceKey: PreferencesKey.currentZcashNodeIdKey,
-          );
+          // Hash Wallet: zcash removed. The original migration here added
+          // zcash node list + set default zcash node. We no longer load
+          // zcash_node_list.yml (it was deleted), so skip the whole step.
+          break;
         case 56:
           await sharedPreferences.setString(
               PreferencesKey.syncStatusDisplayMode, SyncStatusDisplayMode.blocksRemaining.name);