refactor: VM-only architecture — remove tree-walking interpreter

Eliminate dual-engine architecture (Interpreter + Vm) in favor of
a single bytecode VM executor.

- Extract shared types (Value, FunctionProto, Closure, UpvalueObj,
  Runtime trait, NativeFn) into new  module
- Consolidate builtin registration in  — single
   used by VM, eliminates 40-line duplicate
- Delete tree-walker: exec.rs, eval.rs, interpreter.rs, env.rs, module.rs
- Change Value::Function(Rc<Function>) → Value::Function(Rc<Closure>)
  eliminating the closures HashMap pointer-key hack
- Fix VM semantic gaps found during migration:
  * Structural equality for Object/Array in is_equal
  * CompoundAssignGlobal opcode (global compound assigns were broken)
  * 9 string methods added to VM get_property
  * ForInInit error on non-iterable values
- Switch run_file/run_repl to VM; remove --vm CLI flag
- Move 327 tests from interpreter/ to vm/ — all pass

Co-Authored-By: Claude <noreply@anthropic.com>

aster-core/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod lexer;
 pub mod ast;
 pub mod parser;
+pub mod runtime;
 pub mod interpreter;
 pub mod vm;
 pub mod error;
@@ -8,7 +9,6 @@ pub mod analysis;
 
 use lexer::Lexer;
 use parser::Parser;
-use interpreter::Interpreter;
 use vm::compiler::Compiler;
 use vm::vm::Vm;
 use error::RuntimeError;
@@ -37,33 +37,6 @@ pub fn run_file(filename: &str, src: String) {
         std::process::exit(65);
     }
 
-    let script_dir = std::path::Path::new(filename)
-        .parent()
-        .map(|p| p.to_string_lossy().to_string())
-        .unwrap_or_else(|| ".".to_string());
-
-    let mut interpreter = Interpreter::with_current_dir(script_dir);
-    if let Err(e) = interpreter.interpret(stmts) {
-        eprintln!("Error: {}", e);
-        std::process::exit(70);
-    }
-}
-
-/// Run a file using the bytecode VM (for performance comparison).
-pub fn run_file_vm(filename: &str, src: String) {
-    let (tokens, lex_errors) = Lexer::new(&src).tokenize();
-    if !lex_errors.is_empty() {
-        print_errors(&lex_errors);
-        std::process::exit(65);
-    }
-
-    let mut parser = Parser::new(tokens);
-    let (stmts, parse_errors) = parser.parse();
-    if !parse_errors.is_empty() {
-        print_errors(&parse_errors);
-        std::process::exit(65);
-    }
-
     let script_dir = std::path::Path::new(filename)
         .parent()
         .map(|p| p.to_string_lossy().to_string())
@@ -87,9 +60,9 @@ pub fn run_file_vm(filename: &str, src: String) {
 pub fn run_repl() {
     println!("Welcome to Aster REPL!");
     println!("Type ':exit' to quit.");
-    println!("Type ':reset' to reset the interpreter state.");
+    println!("Type ':reset' to reset the VM state.");
 
-    let mut interpreter = Interpreter::new();
+    let mut vm = Vm::new();
     let mut line = String::new();
 
     loop {
@@ -113,8 +86,8 @@ pub fn run_repl() {
                 break;
             }
             ":reset" => {
-                interpreter = Interpreter::new();
-                println!("Interpreter reset.");
+                vm = Vm::new();
+                println!("VM reset.");
                 continue;
             }
             _ => {}
@@ -133,7 +106,14 @@ pub fn run_repl() {
             continue;
         }
 
-        if let Err(e) = interpreter.interpret(stmts) {
+        let proto = match Compiler::compile(&stmts) {
+            Ok(p) => p,
+            Err(e) => {
+                eprintln!("Compile Error: {}", e);
+                continue;
+            }
+        };
+        if let Err(e) = vm.run(std::rc::Rc::new(proto)) {
             eprintln!("Error: {}", e);
         }
     }