Consolidate public project documentation

[Sequela02]

Summary

• establish one canonical integration path, compatibility reference, and durable release policy
• remove duplicated async configuration, partial source lists, and speculative roadmap content
• pin async evidence to certified upstream versions and verify every evidence link
• correct HS256 entropy wording, public-path semantics, and reset-token concurrency guarantees
• align public Javadoc and diagnostics with the documented contracts

Verification

• all local Markdown links resolve
• every public Markdown file has exactly one H1
• 21 pinned upstream GitHub evidence links return successfully
• ./gradlew.bat spotlessApply clean check qualityCheck build javadoc --no-daemon

No runtime authentication behavior changes.