docs: clarify framework documentation authority

[jBernavaPrah]

Summary

• describe phoxal.com only as the project vision and public introduction
• make docs.rs the authority for the published Rust API
• keep framework implementation and architecture details with this repository and its source

Validation

• git diff --check
• rendered both changed READMEs through the GitHub Markdown API
• verified all referenced local paths exist
• verified phoxal.com and docs.rs/phoxal resolve successfully

Risk

Documentation-only change. Runtime behavior, APIs, packaging, and release behavior are unchanged.