Derive picture frame size from picture texture aspect ratio

Replace Width/Height with a single Size (longer side); the shorter side
follows the picture material's base map source-image aspect (editor-
resolved, serialized for builds, 1:1 fallback). Add Range attributes on
all frame parameters and default material references (new Frame.mat).

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

Assets/Materials/Frame.mat.meta

@@ -0,0 +1,8 @@
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