refactor: 拆分 oxide_emit 为独立 emit pass crate（依赖倒置）

crates/oxide_emit/src/stmt/control.rs

@@ -0,0 +1,55 @@
+use crate::{CompileCtx, Emitter};
+use oxide_ir::inst::Inst;
+use oxide_ir::operand::Operand;
+use oxide_bytecode::module::Constant;
+use oxide_bytecode::opcode::OpCode;
+use oxide_parser::Statement;
+
+impl Emitter {
+    fn emit_if_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+        let Statement::IfStatement(ifs) = stmt else {
+            return Ok(None);
+        };
+        let else_label = ctx.next_label_id();
+        let end_label = ctx.next_label_id();
+
+        let test_reg = self.emit_expression(&ifs.test, ctx)?;
+
+        ctx.inst(Inst::jmp_if_false(test_reg, else_label));
+
+        let cons_reg = self.emit_statement(&ifs.consequent, ctx)?;
+        let result_reg = ctx.alloc_reg();
+        if let Some(r) = cons_reg {
+            ctx.inst(Inst::new(OpCode::LOAD_VAR, Operand::Reg(result_reg as u32), Operand::Reg(r as u32), Operand::None));
+        } else {
+            let undef_idx = ctx.add_constant(Constant::Undefined);
+            ctx.inst(Inst::load_const(Operand::Reg(result_reg as u32), undef_idx));
+        }
+
+        if ifs.alternate.is_some() {
+            ctx.inst(Inst::jmp(end_label));
+        }
+
+        ctx.labels.set_label_pos(else_label, ctx.insts.len());
+        if let Some(alt) = &ifs.alternate {
+            let alt_reg = self.emit_statement(alt, ctx)?;
+            if let Some(r) = alt_reg {
+                ctx.inst(Inst::new(OpCode::LOAD_VAR, Operand::Reg(result_reg as u32), Operand::Reg(r as u32), Operand::None));
+            } else {
+                let undef_idx = ctx.add_constant(Constant::Undefined);
+                ctx.inst(Inst::load_const(Operand::Reg(result_reg as u32), undef_idx));
+            }
+        }
+
+        ctx.labels.set_label_pos(end_label, ctx.insts.len());
+
+        Ok(Some(result_reg))
+    }
+
+    pub(crate) fn emit_control_domain(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+        match stmt {
+            Statement::IfStatement(_) => self.emit_if_statement(stmt, ctx),
+            _ => Ok(None),
+        }
+    }
+}