CHANGELOG and README polish for first release

[abienkowski]

Problem

CHANGELOG.md and README.md need a final polish pass before the first release to accurately reflect the current state of the project.

Solution

1. CHANGELOG: finalize [Unreleased] section into a proper versioned entry; verify "Rust implementation with tokio/hyper runtime (88 unit tests)" and other counts are up to date (Rust is now 104)
2. README: verify architecture section, middleware pipeline, endpoint access table, and config examples match the actual implementations
3. Verify the spec README invariants count and any other stale references are corrected
4. Confirm the Repo Standard references (docs/repo-standard.md) are complete

Which implementation(s) would this affect?

• All

Additional context

• Tracked by epic First release prep: Quint spec review, test parity, and release pipeline validation #4