docs(core): sync sealed compatibility version matrix

[kovawx]

Summary

Synchronize the public Core compatibility matrix with the authoritative release/breaking-changes.md in zerodenet/core.

Fixes

• Move the Cargo feature, event ID, Connector contract, and principal-rate changes from Unreleased to their sealed 0.0.15-rc.2 version.
• Add the missing 0.0.15-rc.3 diagnostics and Connector backlog compatibility notes.
• Add explicit 0.0.15-rc.4 and 0.0.15 rows with no compatibility changes.
• Reset Unreleased to indicate that Core 0.0.16-dev.1 currently has no pending compatibility changes.
• Align the release-process wording with the current Prepare Release workflow and scripts/release.sh.

Validation

• Branch starts from the current develop head.
• Diff is limited to docs/projects/core/control-plane/breaking-changes.md.
• Content was compared against the current Core develop compatibility ledger.