refactor: split optimizer/verifier/parser modules (mainline); add runner trace/directives; add LLVM terminator/select scaffolds; extract AST Span; update CURRENT_TASK with remaining plan

src/parser/mod.rs

@@ -19,6 +19,7 @@
 // サブモジュール宣言
 mod common;
 mod expressions;
+mod expr;
 mod statements;
 mod declarations;
 mod items;