VISOR: validate packed-bijou-cells/1 and adapt to Surface

[flyingrobots]

VISOR: validate packed-bijou-cells/1 and adapt to Surface

Define the terminal receipt boundary so Geordi can eventually render directly to the same packed bytes Bijou consumes.

Acceptance Criteria

• packed-bijou-cells/1 is documented as a receipt contract.
• Bijou validates shape, dimensions, glyphs, colors, and focus/chroma metadata.
• A fixture can round-trip into the terminal Surface without hidden normalization.
• Invalid packed-cell receipts fail deterministically.

Parent tracker: #457
VISOR tracker: flyingrobots/visor#1