refactor(audit): batch 7 — RPC/settings/lite/effects mechanical dedups

Six behavior-preserving consolidations from the audit:

- RPCClient::call() overloads share a private performCall() (payload dump +
  curl_easy_perform + http code) and a static parseRpcResult() (error->RpcError
  extraction). The timeout overload restores the prior timeout in both the
  success and catch paths, exactly as before.
- The six UnifiedCallback methods delegate to one splitUnified() that builds
  the (Callback, ErrorCallback) pair once (null-check preserved).
- One liteTrimCopy() in lite_connection_service replaces 5 file-local
  trim-copy helpers across the lite slice.
- lite_wallet_controller's inline height JSON parse now routes through the
  tested parseLiteHeightResponse().
- theme_effects.cpp: unpackRGB()/scaledAlpha() replace 14 RGB-unpack + 5
  alpha-scale copy-paste blocks.
- settings.cpp load() uses loadScalar()/loadClamped() helpers for ~44 scalar
  fields. Besides removing boilerplate this HARDENS loading: ~44 fields that
  previously only checked contains() now also verify the JSON type, so a
  malformed value in settings.json falls back to the default instead of
  throwing/misreading. Custom cases (enum parses, legacy migrations, arrays)
  stay inline; save() is unchanged.

Full-node + Lite build clean; ctest 1/1; hygiene clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/wallet/lite_wallet_gateway.cpp

@@ -1,22 +1,10 @@
 #include "wallet/lite_wallet_gateway.h"
 
-#include <cctype>
 #include <utility>
 
 namespace dragonx::wallet {
 namespace {
 
-std::string trimGatewayCopy(const std::string& value)
-{
-    auto begin = value.begin();
-    while (begin != value.end() && std::isspace(static_cast<unsigned char>(*begin))) ++begin;
-
-    auto end = value.end();
-    while (end != begin && std::isspace(static_cast<unsigned char>(*(end - 1)))) --end;
-
-    return std::string(begin, end);
-}
-
 WalletBackendStatus makeGatewayStatus(WalletBackendState state, std::string message)
 {
     WalletBackendStatus status;
@@ -262,7 +250,7 @@ LiteWalletRefreshResult LiteWalletGateway::refresh(const LiteWalletRefreshReques
 
 LiteServerSelectionResult LiteWalletGateway::selectServerForRequest(const std::string& serverUrl) const
 {
-    const auto overrideUrl = trimGatewayCopy(serverUrl);
+    const auto overrideUrl = liteTrimCopy(serverUrl);
     if (!overrideUrl.empty()) {
         if (!isLiteServerUrlUsable(overrideUrl)) {
             return LiteServerSelectionResult{false, {}, 0, false, "lite gateway server URL is not usable"};