feat: port el-ui vessels — rename crates→vessels, add El source + manifests

ui/vessels/el-ui-compiler/src/error.rs

@@ -0,0 +1,15 @@
+use thiserror::Error;
+
+pub type CompileResult<T> = Result<T, CompileError>;
+
+#[derive(Debug, Error)]
+pub enum CompileError {
+    #[error("lexer error at position {pos}: {msg}")]
+    Lex { pos: usize, msg: String },
+
+    #[error("parse error: {msg}")]
+    Parse { msg: String },
+
+    #[error("codegen error: {msg}")]
+    Codegen { msg: String },
+}