fix(postprocess): demote hollow composite moves after eviction

[HarshK97]

Problem

1. When we demote an outer container move (like an if statement) down to a Delete and Insert, all its inner tokens get evicted. But if an inner composite expression (like a condition binary_expression) had its own Move action, it slipped past our hollow container checks because those only ran on blocks or delimited containers like {} or ().
2. So even when every single payload leaf inside the expression got wiped out by the demotion cascade, the outer expression move survived. That left a hollow move shell that painted the destination code in move color while deleting the whole thing on the source side.

What Changed

• In shouldDemoteMove, check if a composite node had mapped payload leaves that all got evicted by an ancestor demotion cascade, and demote it to Delete and Insert too.
• Checked unevicted leaves first so we can short-circuit on the very first surviving leaf in the normal case, instead of walking the AST descendants twice for every candidate move.
• Added a regression test in internal/postprocess/normalize_test.go to make sure condition expressions inside demoted control flow don't hang around as hollow moves.