Motion rule → Scalar; v2 payload (6×i64 Q32.32), dual decode v1/v2

[flyingrobots]

Port motion rule to use Scalar. Introduce payload v2 (Q32.32) with dual decode to preserve fixtures.

• Golden tests updated for v2; preserve v1 path for compatibility

[flyingrobots]

Implemented motion payload v2 (Q32.32 i64) + dual decode v0/v2 and ported motion executor to Scalar; v0 payloads upgrade to v2 on write (commit 3afe0a3).