docs: add SEO and LLM discoverability baseline

[maxitoon]

Summary

• Rewrites the README title and intro for GitHub/search/LLM discoverability
• Adds use cases, examples, FAQ, alternatives/comparisons, and roadmap sections
• Adds .seo/project-profile.md as the canonical SEO/LLM context source
• Adds llms.txt for LLM crawler/assistant context
• Adds CHANGELOG.md baseline

Verification

• Ran local SEO audit projection: 104/112 (93/100), only missing homepage URL
• Metadata already updated via GitHub API: description + topics

Notes

This is the first project-level pass from the broader GitHub SEO / LLM SEO rollout.

[maxitoon]

CI update from Hermes:

• Python matrix tests are now passing on the latest pushed commit.
• The remaining failing check is the build job before checkout because .github/workflows/ci.yml uses deprecated actions/upload-artifact@v3. GitHub now blocks v3.
• I prepared the fix (actions/upload-artifact@v4), but the available token cannot push workflow-file changes because it lacks the workflow scope.

Required manual/credential step: push this one-line workflow change with a token that has workflow scope, or update it in GitHub UI:

-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4