Version storage namespaces and reject incompatible key migrations explicitly

[Jagadeeshftw]

Problem

Storage key changes can silently reinterpret old data when a new feature reuses an existing namespace.

Scope

Introduce explicit namespace versions and make readers reject or migrate unsupported versions instead of guessing.

Acceptance criteria

• Every changed namespace has a version marker.
• Unsupported versions fail with a stable error.
• Migration tests prove old data is preserved or intentionally transformed.

Validation

Add collision and backward-compatibility tests for representative records.