Add PREDVAL coverage-grid identity

[aRealGem]

Summary

• Add the selected coverage-grid identity as editable, transparent SVG icons and horizontal wordmarks in light/dark variants.
• Add a theme-aware README logo with descriptive alt text; preserve all existing README prose.
• Include concise usage notes and the DejaVu font license. Wordmarks are outlined and have no runtime font dependency.

This is a branding-only branch from main at 4eec9851a4dd31f7795386e89e2282d95e393749, independent of PR #6. No statistical code, tests, fixtures, workflow, or dependency files are changed. No clinical certification is implied.

Verification

• Visually inspected light/dark renders and standalone icons at 32, 128, and 512 px.
• Validated SVG XML, outlined typography, and transparency in local PNG exports.
• Verified the remote tree differs from the base only in the seven expected README/branding files.
• Confirmed that the README change is only a logo insertion; existing prose is byte-for-byte preserved.
• Application tests were not rerun locally for this documentation-only change; GitHub CI will report separately.

Preview exports, ZIPs, and temporary generation files are intentionally not committed.

Co-developed-with: OpenAI Codex