Define the Zeliard 2 art bible and asset specification

[nolanvenhola]

Summary

• define an original visual language rooted in Zeliard's grid-readable play without copying legacy resources
• specify resolution, scaling, tiles, sprite canvases, palettes, silhouettes, animation cadence, typography, lighting, VFX, and HUD rules
• establish measurable accessibility, naming, format, performance-budget, and provenance requirements
• provide concrete acceptance examples for every representative vertical-slice visual family
• document the production workflow, definition of done, and future automated validation codes

Verification

• local Markdown links resolve
• git diff --check passes
• scope is limited to the art bible and links from the accepted product/project documentation

Closes #243