fix(security): harden untrusted-input parsing (Tier 4 audit items)

- export: neutralize CSV/spreadsheet formula injection in transaction export —
  escapeCSV() now prefixes fields beginning with = + - @ / tab / CR with a
  single quote so a hostile memo/address cannot execute on open (F13-1).
- console: preserve explicitly-quoted empty arguments in ParseConsoleCommandArgs
  so a "" no longer collapses and shifts later positional RPC params; adds a
  regression assertion to testConsoleInputModel (F14-1).
- send: copy pending payment-URI address/memo with snprintf("%s") instead of
  strncpy(…, sizeof-1), which does not NUL-terminate on truncation (F8-2).

All build clean (full-node + tests) and the suite passes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_phase4.cpp

@@ -2378,6 +2378,12 @@ void testConsoleInputModel()
     auto args = dragonx::ui::ParseConsoleCommandArgs("z_sendmany \"from addr\" [{\"address\":\"zs\",\"amount\":1.25}] true");
     EXPECT_EQ(args.size(), static_cast<size_t>(4));
     EXPECT_EQ(args[1], std::string("from addr"));
+    // An explicitly-quoted empty argument must be preserved (not dropped), otherwise
+    // later positional RPC params silently shift by one (F14-1).
+    auto emptyArgs = dragonx::ui::ParseConsoleCommandArgs("walletpassphrase \"\" 60");
+    EXPECT_EQ(emptyArgs.size(), static_cast<size_t>(3));
+    EXPECT_EQ(emptyArgs[1], std::string(""));
+    EXPECT_EQ(emptyArgs[2], std::string("60"));
     auto call = dragonx::ui::BuildConsoleRpcCall("setgenerate true 4");
     EXPECT_TRUE(call.valid);
     EXPECT_EQ(call.method, std::string("setgenerate"));