docs: update ROADMAP and LanguageRef with closures

- Mark capture-less closures as ✅ Done in ROADMAP
- Add closure syntax examples to LanguageRef.md Functions section
- Update PHASE8_STRATEGY.md Milestone A with closures

docs/PHASE8_STRATEGY.md

@@ -294,6 +294,7 @@ Crates.io е непреодолимо предимство. Ние се конк
 - ✅ defer, switch/case, operator overloading — готово
 - ✅ `bux new`, `bux init`, `bux test`, `bux fmt` — готово
 - ✅ Basic borrow checker (`@[Checked]`) — готово
+- ✅ Closures (capture-less anonymous functions) — готово
 - 🎯 Target: Можеш да напишеш `bux` package manager на Bux
 
 ### Milestone B: "Използваем за systems programming" (2 месеца)