fix(release): restore the unreleased 0.6.0 train

[Fieldnote-Echo]

What changed

• restore every lockstep Rust and Python package version from the erroneous unreleased 0.7.0 metadata to 0.6.0
• restore the README dependency example and threat-model status to 0.6.0
• collapse the two unpublished changelog sections into one 0.6.0 release section
• state the public 0.5.x manifest-v1 compatibility break accurately
• replace the stale OrdinalDB branch-specific un-patch note with the real root plus standalone-consumer release gate
• regenerate the root and fuzz lockfiles at 0.6.0

Why

Neither 0.6.0 nor 0.7.0 has been published or tagged; registries still serve 0.5.0. The schema-v2 and typed-verification work is unreleased work for the intended 0.6.0 train, so the later 0.7.0 release metadata was premature.

This is a forward metadata correction. It deliberately keeps the schema-v2 implementation and all post-0.5.0 hardening; it does not rewrite history or back-release an older commit.

Impact

Downstream consumers such as OrdinalDB can continue targeting the intended ordvec = "0.6.0" and ordvec-manifest = "0.6.0" APIs and schema-v2 behavior once the release is published.

Validation

• python3 tests/release_publish_invariants.py
• bash tests/release_signed_release_invariants.sh
• cargo package -p ordvec --locked --allow-dirty
• core tests: default, experimental, test-utils, and no-default-features
• manifest tests: no-default-features and all-features
• FFI build and tests
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• cargo deny check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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