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-core/src/ast/expr.rs

@@ -0,0 +1,141 @@
+use crate::ast::stmt::Stmt;
+
+#[derive(Debug, Clone)]
+pub enum Expr {
+    /// 字面量：number / string / bool / nil
+    Literal(Literal),
+
+    /// 变量引用
+    Variable(String),
+
+    /// 赋值表达式：a = b
+    Assign {
+        name: String,
+        op: AssignOp,
+        value: Box<Expr>,
+    },
+
+    /// 属性访问表达式：object.name
+    Get {
+        object: Box<Expr>,
+        name: String,
+    },
+
+    /// 属性赋值表达式：object.name = value
+    Set {
+        object: Box<Expr>,
+        name: String,
+        op: AssignOp,
+        value: Box<Expr>,
+    },
+
+    /// 对象字面量：{ key: value, ... }
+    ObjectLiteral {
+        properties: Vec<(String, Expr)>,
+    },
+
+    /// 数组字面量：[ expr, expr, ... ]
+    ArrayLiteral {
+        elements: Vec<Expr>,
+    },
+
+    /// 索引访问：expr[index]
+    IndexGet {
+        array: Box<Expr>,
+        index: Box<Expr>,
+    },
+
+    /// 索引赋值：expr[index] = value
+    IndexSet {
+        array: Box<Expr>,
+        index: Box<Expr>,
+        op: AssignOp,
+        value: Box<Expr>,
+    },
+
+    /// 一元运算：!expr / -expr
+    Unary {
+        op: UnaryOp,
+        right: Box<Expr>,
+    },
+
+    /// 二元运算：a + b
+    Binary {
+        left: Box<Expr>,
+        op: BinaryOp,
+        right: Box<Expr>,
+    },
+
+    /// 逻辑运算：&& ||
+    Logical {
+        left: Box<Expr>,
+        op: LogicalOp,
+        right: Box<Expr>,
+    },
+
+    /// 三元运算：condition ? then_branch : else_branch
+    Ternary {
+        condition: Box<Expr>,
+        then_branch: Box<Expr>,
+        else_branch: Box<Expr>,
+    },
+
+    /// 函数调用
+    Call {
+        callee: Box<Expr>,
+        arguments: Vec<Expr>,
+    },
+
+    /// 匿名函数（为闭包预留）
+    Lambda {
+        params: Vec<String>,
+        body: Vec<Stmt>,
+    },
+}
+
+#[derive(Debug, Clone)]
+pub enum Literal {
+    Number(f64),
+    String(String),
+    Bool(bool),
+    Nil,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum UnaryOp {
+    Negate, // -
+    Not,    // !
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum BinaryOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Mod,
+
+    Greater,
+    GreaterEqual,
+    Less,
+    LessEqual,
+
+    Equal,
+    NotEqual,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum LogicalOp {
+    And,
+    Or,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum AssignOp {
+    Equal,      // =
+    PlusEqual,  // +=
+    MinusEqual, // -=
+    StarEqual,  // *=
+    SlashEqual, // /=
+    PercentEqual, // %=
+}