docs(readme): replace rock logo with light mark

[code-yeongyu]

Summary

Replace the rock logo at the top of the LazyCodex README with the new
Sisyphus Labs light OmO mark.

Changes

• Add the exact omo-icon-light.svg source asset.
• Point the root README at the new SVG.
• Record manual render and link-resolution QA evidence.

QA & Evidence

• What was tested: source hash equality, XML parsing, README path
  resolution, and a 512 px Quick Look render.
• Observed result: the committed SVG matches source SHA-256
  0cb99c9fc750827f2c35ae99659de6d40e03ae7b1d79d3c29f1002017fe33b0a;
  the README path resolves; the render showed the complete dark OmO cat mark
  on the light rounded-square background without clipping.
• Artifact: .omo/evidence/20260809-readme-light-logo/qa.md
• Why sufficient: this covers source integrity, markup validity, broken-link
  risk, and the actual user-visible render.

Risks & Residuals

• Documentation and image asset only. No runtime behavior changes.

---

Summary by cubic

Replaces the README’s rock logo with the Sisyphus Labs light OmO mark using omo-icon-light.svg for sharper, scalable rendering. Adds the SVG asset and QA evidence verifying integrity, valid XML, correct README path, and correct render.

^{Written for commit 10f9558. Summary will update on new commits.}

[github-actions]

Thanks for the PR! Changes to LazyCodex land through oh-my-openagent — could you open this against omo-codex over there instead? PRs in this repository can't be merged.

If you're working with a coding agent, prompt it like this:

I opened #156 ("docs(readme): replace rock logo with light mark") against code-yeongyu/lazycodex, but changes there land through code-yeongyu/oh-my-openagent, where the Codex implementation lives under packages/omo-codex. Read my original PR, then open an equivalent PR against code-yeongyu/oh-my-openagent. In the new PR body, link the original PR (#156), explain that it was first opened against lazycodex, and describe in detail what that PR changed and why.