refactor: sema.c + codegen.c 拆分，全部源文件 <800 行

sema.c 1129行 → sema.c 499行 + typeck.c 629行 + sema_internal.h 51行
  - typeck.c: 表达式类型检查 (10个analyze_*函数) + 泛型单态化 + 类型关系
  - sema.c: analyze_node + sema_analyze

codegen.c 947行 → codegen.c 453行 + cg_expr.c 440行 + codegen_internal.h 83行
  - cg_expr.c: LLVM表达式生成 + 类型映射 (to_llvm_type/coerce_int/type_info_to_llvm)
  - codegen.c: 语句生成 + 模块入口 + 符号表 + 内存清理

全部核心源文件 <800 行限制: parser(662+498), sema(499+629), codegen(453+440)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/codegen/codegen_internal.h

@@ -0,0 +1,83 @@
+#ifndef CODEGEN_INTERNAL_H
+#define CODEGEN_INTERNAL_H
+
+#include "codegen.h"
+#include "ast.h"
+#include "arena.h"
+#include "l_lang.h"
+#include <llvm-c/Analysis.h>
+#include <llvm-c/Types.h>
+#include <string.h>
+#include <stdio.h>
+
+// 递归深度限制
+extern int codegen_depth;
+#define MAX_CODEGEN_DEPTH 1000
+
+// === 内部状态 ===
+typedef struct VarEntry {
+    const char*       name;
+    LLVMValueRef      alloca;
+    LLVMTypeRef       alloca_type;
+    struct VarEntry*  next;
+} VarEntry;
+
+typedef struct FnEntry {
+    const char*       name;
+    LLVMValueRef      fn;
+    TypeKind          ret;
+    TypeKind*         params;
+    size_t            pc;
+    struct FnEntry*   next;
+} FnEntry;
+
+typedef struct StructTypeEntry {
+    const char*             name;
+    LLVMTypeRef             llvm_type;
+    size_t                  field_count;
+    struct StructTypeEntry* next;
+} StructTypeEntry;
+
+typedef struct {
+    Arena*            arena;
+    LLVMContextRef    context;
+    LLVMModuleRef     module;
+    LLVMBuilderRef    builder;
+    VarEntry*         var_table;
+    const char*       error;
+    FnEntry*          fn_table;
+    StructTypeEntry*  struct_table;
+    LLVMValueRef      printf_fn;
+    LLVMTypeRef       printf_ty;
+    LLVMValueRef      malloc_fn;
+    LLVMValueRef      free_fn;
+    LLVMValueRef      strlen_fn;
+    LLVMValueRef      memcpy_fn;
+    LLVMValueRef*     cleanup_list;
+    size_t            cleanup_count;
+    size_t            cleanup_cap;
+} CgCtx;
+
+// === 类型映射 ===
+LLVMTypeRef to_llvm_type(CgCtx* ctx, TypeKind kind);
+LLVMValueRef to_llvm_const(LLVMTypeRef ty, AstNode* lit);
+LLVMTypeRef type_info_to_llvm(CgCtx* ctx, const TypeInfo* ti);
+LLVMValueRef coerce_int(CgCtx* ctx, LLVMValueRef val, LLVMTypeRef from_ty, LLVMTypeRef to_ty);
+
+// === 表操作 ===
+LLVMValueRef find_var(CgCtx* ctx, const char* name);
+void add_var(CgCtx* ctx, const char* name, LLVMValueRef alloca, LLVMTypeRef alloca_type);
+LLVMValueRef find_fn(CgCtx* ctx, const char* name);
+void add_fn(CgCtx* ctx, const char* name, LLVMValueRef fn);
+void add_struct_type(CgCtx* ctx, const char* name, LLVMTypeRef ty, size_t fc);
+LLVMTypeRef find_struct_type(CgCtx* ctx, const char* name);
+
+// === 内存清理 ===
+void cleanup_add(CgCtx* ctx, LLVMValueRef alloca);
+void cleanup_emit(CgCtx* ctx, size_t from_mark);
+
+// === 代码生成函数 ===
+LLVMValueRef codegen_expr(CgCtx* ctx, AstNode* node);
+void codegen_stmt(CgCtx* ctx, AstNode* node);
+
+#endif