fix(compiler): skip auto-Drop after field/let/return moves

Track locals moved by value into struct fields, let bindings, or return
values so Array/Drop types are not freed while still owned by the target.

- hir_lower: movedOutLocals + markMovedOutFromAst + shouldSkipDrop
- Nexus: drop zeroing workaround; free headers after each request
- examples/move_field.bux regression for Box { items: arr }

docs/QUALITY_PLAN.md

@@ -1,7 +1,7 @@
 # Bux — План към „добър“ език (v0.5 → v1.0)
 
 > **Дата:** 2026-07-19  
-> **Текущо:** v0.5.x — Nexus keep-alive, **header Array ownership fix**, LSP 0.6 workspace/symbol, selfhost `-g`  
+> **Текущо:** v0.5.x — **field-move skip Drop**, Nexus keep-alive, LSP 0.6, selfhost `-g`  
 > **Цел:** Език, с който се пишат реални проекти комфортно, безопасно (по избор) и с надежден toolchain.
 
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