improve E004 card generation and placeholder pcbid (#748)

## Link to GitHub Issue or related Pull Request, if one exists
#73

## Description of change
Generated cards now start with E0040100 to fully match real cards. The
placeholder example `E004010000000000` is replaced with
`E0040100FFFFFFFF`.

The invalid placeholder/fallback PCBID `04040000000000000000` is
replaced with `01201000000000010101`, which contains a valid
header/checksum, making it closer resemble a real PCBID while still
clearly being an example.

src/spice2x/overlay/windows/card_manager.cpp

@@ -166,7 +166,7 @@ namespace overlay::windows {
         if (ImGui::BeginPopupModal("Card Editor", nullptr, ImGuiWindowFlags_AlwaysAutoResize)) {
             // card ID field (only editable for new cards)
             ImGui::BeginDisabled(this->current_card);
-            ImGui::InputTextWithHint("Card ID", "E0040123456789AB",
+            ImGui::InputTextWithHint("Card ID", "E0040100FFFFFFFF",
                     this->card_buffer,
                     std::size(this->card_buffer),
                     ImGuiInputTextFlags_CharsHexadecimal | ImGuiInputTextFlags_CharsUppercase);