feat: restructure repo, borrow checker, expanded stdlib

- Reorganize repository to Rust-style layout:
  compiler/bootstrap/  compiler/selfhost/  compiler/tests/
  library/std/  library/runtime/  tests/  tools/
- Add buxs/ Windows-compatible project root
- Add borrow checker tests and implement:
  - Alias analysis (double mutable borrow detection)
  - Use-after-move detection for own T
- Expand standard library:
  - Std::Os: Args, Env, Cwd, Chdir
  - Std::Time: NowMs, NowUs, SleepMs
  - Std::Process: Run, Output
  - Std::Io: PrintInt64 (fixes 32-bit truncation bug)
- Add examples: os_time.bux, process.bux
- Fix PrintInt to use int64_t in C runtime

compiler/selfhost/types.bux

@@ -0,0 +1,188 @@
+// types.bux — Type system definitions and factories
+module Types {
+
+// ---------------------------------------------------------------------------
+// TypeKind constants
+// ---------------------------------------------------------------------------
+
+const tyUnknown: int = 0;
+const tyVoid: int = 1;
+const tyBool: int = 2;
+const tyBool8: int = 3;
+const tyBool16: int = 4;
+const tyBool32: int = 5;
+const tyChar8: int = 6;
+const tyChar16: int = 7;
+const tyChar32: int = 8;
+const tyStr: int = 9;
+const tyInt8: int = 10;
+const tyInt16: int = 11;
+const tyInt32: int = 12;
+const tyInt64: int = 13;
+const tyInt: int = 14;
+const tyUInt8: int = 15;
+const tyUInt16: int = 16;
+const tyUInt32: int = 17;
+const tyUInt64: int = 18;
+const tyUInt: int = 19;
+const tyFloat32: int = 20;
+const tyFloat64: int = 21;
+const tyPointer: int = 22;
+const tySlice: int = 23;
+const tyRange: int = 24;
+const tyTuple: int = 25;
+const tyNamed: int = 26;
+const tyTypeParam: int = 27;
+const tyFunc: int = 28;
+
+// ---------------------------------------------------------------------------
+// Type struct
+// ---------------------------------------------------------------------------
+
+struct Type {
+    kind: int;
+    name: String;
+    // inner types stored as array of pointers (simplified)
+    innerKind1: int;
+    innerName1: String;
+    innerKind2: int;
+    innerName2: String;
+    innerKind3: int;
+    innerName3: String;
+    innerCount: int;
+}
+
+// ---------------------------------------------------------------------------
+// Factories
+// ---------------------------------------------------------------------------
+
+func Type_MakeUnknown() -> Type {
+    return Type { kind: tyUnknown, name: "", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeVoid() -> Type {
+    return Type { kind: tyVoid, name: "void", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeBool() -> Type {
+    return Type { kind: tyBool, name: "bool", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeInt() -> Type {
+    return Type { kind: tyInt, name: "int", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeInt64() -> Type {
+    return Type { kind: tyInt64, name: "int64", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeUInt() -> Type {
+    return Type { kind: tyUInt, name: "uint", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeFloat64() -> Type {
+    return Type { kind: tyFloat64, name: "float64", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeStr() -> Type {
+    return Type { kind: tyStr, name: "String", innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakePointer(pointee: Type) -> Type {
+    return Type { kind: tyPointer, name: "", innerCount: 1,
+        innerKind1: pointee.kind, innerName1: pointee.name,
+        innerKind2: 0, innerName2: "", innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeNamed(name: String) -> Type {
+    return Type { kind: tyNamed, name: name, innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+func Type_MakeTypeParam(name: String) -> Type {
+    return Type { kind: tyTypeParam, name: name, innerCount: 0,
+        innerKind1: 0, innerName1: "", innerKind2: 0, innerName2: "",
+        innerKind3: 0, innerName3: "" };
+}
+
+// ---------------------------------------------------------------------------
+// Predicates
+// ---------------------------------------------------------------------------
+
+func Type_IsNumeric(t: Type) -> bool {
+    let k: int = t.kind;
+    if k == tyInt8 || k == tyInt16 || k == tyInt32 || k == tyInt64 || k == tyInt { return true; }
+    if k == tyUInt8 || k == tyUInt16 || k == tyUInt32 || k == tyUInt64 || k == tyUInt { return true; }
+    if k == tyFloat32 || k == tyFloat64 { return true; }
+    if k == tyUnknown || k == tyNamed || k == tyTypeParam { return true; }
+    return false;
+}
+
+func Type_IsInteger(t: Type) -> bool {
+    let k: int = t.kind;
+    if k == tyInt8 || k == tyInt16 || k == tyInt32 || k == tyInt64 || k == tyInt { return true; }
+    if k == tyUInt8 || k == tyUInt16 || k == tyUInt32 || k == tyUInt64 || k == tyUInt { return true; }
+    if k == tyUnknown || k == tyNamed || k == tyTypeParam { return true; }
+    return false;
+}
+
+func Type_IsBool(t: Type) -> bool {
+    let k: int = t.kind;
+    return k == tyBool || k == tyBool8 || k == tyBool16 || k == tyBool32;
+}
+
+func Type_IsPointer(t: Type) -> bool {
+    return t.kind == tyPointer;
+}
+
+func Type_IsSlice(t: Type) -> bool {
+    return t.kind == tySlice;
+}
+
+// ---------------------------------------------------------------------------
+// Comparison (structural, limited to kind + name for simplicity)
+// ---------------------------------------------------------------------------
+
+func Type_Eq(a: Type, b: Type) -> bool {
+    if a.kind != b.kind { return false; }
+    if a.kind == tyNamed || a.kind == tyTypeParam {
+        return String_Eq(a.name, b.name);
+    }
+    return true;
+}
+
+// ---------------------------------------------------------------------------
+// toString
+// ---------------------------------------------------------------------------
+
+func Type_ToString(t: Type) -> String {
+    if t.kind == tyVoid { return "void"; }
+    if t.kind == tyBool { return "bool"; }
+    if t.kind == tyStr { return "String"; }
+    if t.kind == tyInt { return "int"; }
+    if t.kind == tyInt64 { return "int64"; }
+    if t.kind == tyUInt { return "uint"; }
+    if t.kind == tyFloat64 { return "float64"; }
+    if t.kind == tyNamed { return t.name; }
+    if t.kind == tyTypeParam { return t.name; }
+    if t.kind == tyPointer { return String_Concat("*", t.innerName1); }
+    return "?";
+}
+}