chore(spwkit): prepare v0.7.0 release

[Inczert]

Prepare SpWKit v0.7.0 from the exact post-#227 develop lineage.

This release-preparation PR:

• bumps the project/public API contract to 0.7.0 and installed consumers to the 0.7 package line;
• finalizes the v0.7.0 changelog, release notes, README and current-status material;
• carries the v0.7 runtime/backend-contract hardening, backend-equivalence and scoped ECSS-E-ST-50-12C Rev.1 software-conformance boundary into the release metadata;
• freezes performance evidence against immutable v0.6.1 and the final release-preparation candidate before Complete v0.7.0 ECSS software-conformance and performance release gate #224 is closed;
• introduces no new runtime feature work.

#224 remains the final tag gate until the exact release candidate is tied to green evidence.