fix(lite): import-key fallback on mis-routed key + clamp shield fee

- importKey routed transparent vs. shielded purely by the first character, which
  can mis-route (e.g. testnet/regtest WIFs). On failure, try the other import
  command before reporting an error (each validates the encoding, so a wrong
  command rejects rather than mis-imports). The key copy is wiped after both tries.
- Clamp the shield dialog's fee input to [0, 1] DRGX, mirroring the UTXO-limit
  clamp, so a negative or fat-fingered huge fee can't be submitted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/windows/shield_dialog.cpp

@@ -138,6 +138,8 @@ void ShieldDialog::render(App* app)
         ImGui::Text("%s", TR("fee_label"));
         ImGui::SetNextItemWidth(feeInput.width);
         ImGui::InputDouble("##Fee", &s_fee, 0.0001, 0.001, "%.8f");
+        if (s_fee < 0.0) s_fee = 0.0;          // no negative fee
+        if (s_fee > 1.0) s_fee = 1.0;          // guard a fat-fingered huge fee (mirrors utxo clamp)
         ImGui::SameLine();
         ImGui::TextDisabled("DRGX");