feat: IDE支持 — workspace拆分、LSP服务器、VS Code扩展

**Workspace 拆分**
- aster-core: 纯库，zero-dependency，包含 lexer/parser/ast/interpreter/error/analysis
- aster: REPL 二进制，薄封装 aster-core
- aster-lsp: LSP 语言服务器

**VS Code 扩展 (vscode-ext/)**
- TextMate 语法高亮 (.ast 文件)
- 语言配置 (注释切换、括号配对、自动缩进)
- LSP 客户端 (extension.js)

**LSP 服务端功能**
- Diagnostics: 实时显示 lex/parse 错误红色波浪线
- Completion: 关键字 + 内置函数 + 用户定义符号补全
- Hover: 悬停显示变量/函数信息
- Signature Help: 函数参数提示
- Goto Definition: Ctrl+Click 跳转到声明处
- Find References: 查找所有引用位置
- Rename: F2 重命名符号

**新增 analysis 模块**
- collect_symbols: AST 遍历收集符号
- find_declaration/find_all_references: Token 扫描定位声明和引用

aster/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "aster"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aster-core = { path = "../aster-core" }

aster/src/main.rs

@@ -0,0 +1,24 @@
+use std::env;
+use std::fs;
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+
+    match args.len() {
+        1 => aster_core::run_repl(),
+        2 => {
+            let filename = &args[1];
+            match fs::read_to_string(filename) {
+                Ok(src) => aster_core::run_file(filename, src),
+                Err(e) => {
+                    eprintln!("Error reading file '{}': {}", filename, e);
+                    std::process::exit(1);
+                }
+            }
+        }
+        _ => {
+            eprintln!("Usage: aster [script]");
+            std::process::exit(1);
+        }
+    }
+}