v0.3.0: restructure directories

- src/        ← compiler/selfhost/  (canonical Bux compiler)
- bootstrap/  ← compiler/bootstrap/ (Nim bootstrap)
- lib/        ← library/std/        (standard library)
- rt/         ← library/runtime/    (C runtime)
- tests/      ← compiler/tests/     (unit tests)
- Remove _selfhost/ (built into build/selfhost/ now)
- Update all path references (Makefile, cli.nim, cli.bux, docs)
- Bump version to 0.3.0

tests/parser_test.nim

@@ -0,0 +1,122 @@
+import std/[unittest, os, strutils]
+import ../bootstrap/[lexer, parser, ast, token]
+
+proc parseSource(source: string): ParseResult =
+  let lexRes = tokenize(source, "<test>")
+  check not lexRes.hasErrors
+  result = parse(lexRes.tokens, "<test>")
+
+suite "Parser":
+  test "empty module":
+    let res = parseSource("")
+    check res.diagnostics.len == 0
+    check res.module.items.len == 0
+
+  test "simple function":
+    let res = parseSource("func Main() -> int { return 0; }")
+    check res.diagnostics.len == 0
+    check res.module.items.len == 1
+    check res.module.items[0].kind == dkFunc
+    check res.module.items[0].declFuncName == "Main"
+
+  test "function with parameters":
+    let res = parseSource("func Add(a: int32, b: int32) -> int32 { return a + b; }")
+    check res.diagnostics.len == 0
+    check res.module.items[0].declFuncParams.len == 2
+    check res.module.items[0].declFuncParams[0].name == "a"
+    check res.module.items[0].declFuncParams[1].name == "b"
+
+  test "struct declaration":
+    let res = parseSource("struct Point { x: float64; y: float64; }")
+    check res.diagnostics.len == 0
+    check res.module.items[0].kind == dkStruct
+    check res.module.items[0].declStructName == "Point"
+    check res.module.items[0].declStructFields.len == 2
+
+  test "enum declaration":
+    let res = parseSource("enum Color { Red, Green, Blue }")
+    check res.diagnostics.len == 0
+    check res.module.items[0].kind == dkEnum
+    check res.module.items[0].declEnumName == "Color"
+    check res.module.items[0].declEnumVariants.len == 3
+
+  test "import declaration":
+    let res = parseSource("import Std::Io::PrintLine;")
+    check res.diagnostics.len == 0
+    check res.module.items[0].kind == dkUse
+    check res.module.items[0].declUsePath == @["Std", "Io", "PrintLine"]
+
+  test "const declaration":
+    let res = parseSource("const PI: float64 = 3.14;")
+    check res.diagnostics.len == 0
+    check res.module.items[0].kind == dkConst
+    check res.module.items[0].declConstName == "PI"
+
+  test "type alias":
+    let res = parseSource("type MyInt = int32;")
+    check res.diagnostics.len == 0
+    check res.module.items[0].kind == dkTypeAlias
+    check res.module.items[0].declAliasName == "MyInt"
+
+  test "let statement in function":
+    let res = parseSource("func Main() -> int { let x: int32 = 42; return x; }")
+    check res.diagnostics.len == 0
+    check res.module.items[0].declFuncBody.stmts.len == 2
+    check res.module.items[0].declFuncBody.stmts[0].kind == skLet
+    check res.module.items[0].declFuncBody.stmts[0].stmtLetName == "x"
+
+  test "if statement":
+    let res = parseSource("func Main() -> int { if true { return 1; } else { return 0; } }")
+    check res.diagnostics.len == 0
+    let body = res.module.items[0].declFuncBody
+    check body.stmts[0].kind == skIf
+    check body.stmts[0].stmtIfThen.stmts.len == 1
+    check body.stmts[0].stmtIfElse.stmts.len == 1
+
+  test "while loop":
+    let res = parseSource("func Main() -> int { while true { break; } return 0; }")
+    check res.diagnostics.len == 0
+    let body = res.module.items[0].declFuncBody
+    check body.stmts[0].kind == skWhile
+    check body.stmts[0].stmtWhileBody.stmts[0].kind == skBreak
+
+  test "for loop":
+    let res = parseSource("func Main() -> int { for i in items { continue; } return 0; }")
+    check res.diagnostics.len == 0
+    let body = res.module.items[0].declFuncBody
+    check body.stmts[0].kind == skFor
+    check body.stmts[0].stmtForVar == "i"
+
+  test "match expression":
+    let res = parseSource("func Main() -> int { let x = match 1 { 1 => 10, _ => 20 }; return x; }")
+    check res.diagnostics.len == 0
+    let body = res.module.items[0].declFuncBody
+    check body.stmts[0].kind == skLet
+    check body.stmts[0].stmtLetInit.kind == ekMatch
+
+  test "binary expression":
+    let res = parseSource("func Main() -> int { return 1 + 2 * 3; }")
+    check res.diagnostics.len == 0
+    let ret = res.module.items[0].declFuncBody.stmts[0]
+    check ret.kind == skReturn
+    check ret.stmtReturnValue.kind == ekBinary
+    # 1 + (2 * 3)
+    check ret.stmtReturnValue.exprBinaryOp == tkPlus
+
+  test "call expression":
+    let res = parseSource("func Main() -> int { return Add(10, 20); }")
+    check res.diagnostics.len == 0
+    let ret = res.module.items[0].declFuncBody.stmts[0]
+    check ret.stmtReturnValue.kind == ekCall
+    check ret.stmtReturnValue.exprCallCallee.kind == ekIdent
+
+  test "full sample file":
+    let source = readFile(currentSourcePath.parentDir / "testdata" / "sample.bux")
+    let lexRes = tokenize(source, "sample.bux")
+    check not lexRes.hasErrors
+    let parseRes = parse(lexRes.tokens, "sample.bux")
+    check parseRes.diagnostics.len == 0
+    check parseRes.module.items.len == 3
+    check parseRes.module.items[0].kind == dkUse
+    check parseRes.module.items[1].kind == dkFunc
+    check parseRes.module.items[2].kind == dkFunc