fix(engine): restore cursor position after Call returns

[zharinov]

Summary

• Fix recursive quantified patterns breaking outer sequence matching
• Save cursor position in Frame after Call navigation, restore on Return
• Ensures Nav::Next in quantifier loops finds correct sibling

Root Cause: After a Call instruction returns, cursor was left wherever callee left it (potentially deep in subtree). Outer quantifier's Nav::Next navigated from wrong tree depth.

Test plan

• All 751 existing tests pass
• Recursive query (closure (Rec)*) now returns all matching siblings