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/lexer/token.rs

@@ -0,0 +1,51 @@
+// lexer/token.rs
+#[derive(Debug, Clone, PartialEq)]
+pub enum TokenKind {
+    // 单字符
+    LeftParen, RightParen,
+    LeftBrace, RightBrace,
+    LeftBracket, RightBracket,
+    Comma, Semicolon, Dot,
+    Colon,
+    Question,
+
+    // 运算符
+    Plus, Minus, Star, Slash, Percent,
+    Bang,
+    Equal,
+    Greater, GreaterEqual,
+    Less, LessEqual,
+    EqualEqual, BangEqual,
+    AndAnd, OrOr,
+    PlusEqual, MinusEqual, StarEqual, SlashEqual, PercentEqual,
+
+    // 字面量
+    Identifier(String),
+    Number(f64),
+    String(String),
+
+    // 关键字
+    Let,
+    Const,
+    Fn,
+    If,
+    Else,
+    While,
+    For,
+    In,
+    Break,
+    Continue,
+    Return,
+    True,
+    False,
+    Nil,
+
+    EOF,
+}
+
+#[derive(Debug, Clone)]
+pub struct Token {
+    pub kind: TokenKind,
+    pub line: usize,
+    pub column: usize,
+}