docs: sync all docs with recent features

Updated documentation to reflect changes from the last 2 days:

ROADMAP.md:
- Mark string interpolation, named/default params, bux fmt/test/new/init,
  and basic borrow checker as ✅ Done
- Update Recommended Order (next: closures)

PHASE8_STRATEGY.md:
- Update date, achievements, and milestone statuses
- Borrow checker is now ✅ working in selfhost
- CTFE, LSP, formatter, test runner marked done where applicable

LanguageRef.md:
- Add defer, switch/case, string interpolation (f"...")
- Add &T, &mut T, own T to composite types
- Add named/default parameters and operator overloading sections
- Expand @[Checked] rules with double-mut-borrow and use-after-move
- Update keywords and operators

STRATEGY.md:
- Update date and version (0.3.0 selfhost)
- Mark 8.2 borrow checker, 8.4 CTFE, 8.7 LSP as ✅

BuildAndTest.md:
- Add bux init, bux fmt, bux test commands
- Expand test sections with golden tests and Std::Test

docs/STRATEGY.md

@@ -1,6 +1,6 @@
 # Как Bux ще победи Rust, Nim и C
 
-> **Дата:** 2026-05-31 | **Версия:** 0.2.0 (bootstrap)
+> **Дата:** 2026-06-09 | **Версия:** 0.3.0 (selfhost)
 
 ---
 
@@ -124,12 +124,12 @@ match x { Ok(v) => ..., Err(e) => ... }
 | Фаза | Feature | Ефект |
 |------|---------|-------|
 | **8.1** | ✅ Error handling (`?`, `!`) | По-чисто от Nim |
-| **8.2** | ⏳ `@[Checked]` borrow checker | **Уникално — това е оръжието** |
-| **8.3** | ⏳ Concurrency (tasks + channels) | Go-стил леки нишки |
-| **8.4** | ⏳ CTFE (`const func`) | Nim-level метапрограмиране |
+| **8.2** | ✅ `@[Checked]` borrow checker (basic) | **Уникално — това е оръжието** |
+| **8.3** | 🔄 Concurrency (tasks + channels) | Go-стил леки нишки |
+| **8.4** | ✅ CTFE (`const func`) | Nim-level метапрограмиране |
 | **8.5** | ⏳ Trait система | Rust-стил генерици |
 | **8.6** | ⏳ Макроси | Nim-стил метапрограмиране |
-| **8.7** | ⏳ LSP сървър | IDE поддръжка |
+| **8.7** | ✅ LSP сървър | IDE поддръжка |
 
 ---