card harness dynamic changes

spikes/card-harness/public/card-art/README.md

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+# Card Art Drop Folder
+
+Add each card as one PNG artwork and one matching PNG finish mask:
+
+```text
+david.png
+david-mask.png
+```
+
+The filename before `.png` is the card name shown in the harness. Names are
+case-sensitive. Artwork and mask must:
+
+- have identical dimensions;
+- use a 5:7 aspect ratio;
+- be fully opaque;
+- use an opaque grayscale mask.
+
+During `npm run dev`, adding or replacing either PNG refreshes the searchable
+card catalog automatically. Reopening or focusing the Card field also forces a
+rescan. Production builds generate `manifest.json` from this folder and fail if
+any pair is missing or invalid.