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

crates/oxide_emit/src/expr/mod.rs

@@ -0,0 +1,31 @@
+use crate::{CompileCtx, Emitter};
+use oxide_parser::Expression;
+
+pub mod assignment;
+pub mod call;
+pub mod function;
+pub mod identifier;
+pub mod literal;
+pub mod member;
+pub mod object;
+pub mod operator;
+pub mod parenthesized;
+pub mod template;
+pub mod this;
+
+impl Emitter {
+    pub(crate) fn emit_unsupported_expression(&self, expr: &Expression, ctx: &mut CompileCtx) -> Result<u8, String> {
+        let _ = ctx;
+        Err(format!("unsupported expression type: {:?}", expr))
+    }
+
+    pub(crate) fn emit_sequence_expression(
+        &self, seq: &oxide_parser::SequenceExpression, ctx: &mut CompileCtx,
+    ) -> Result<u8, String> {
+        let mut last = 0u8;
+        for e in &seq.expressions {
+            last = self.emit_expression(e, ctx)?;
+        }
+        Ok(last)
+    }
+}