feat: add List.sort and List.sortBy functions (issue 9)

Add sorting support to the List module across all backends:
- List.sort for natural ordering (Int, Float, String, Bool, Char)
- List.sortBy for custom comparator-based sorting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/codegen/js_backend.rs

@@ -1812,6 +1812,18 @@ impl JsBackend {
                     end, start, start
                 ))
             }
+            "sort" => {
+                let list = self.emit_expr(&args[0])?;
+                Ok(format!(
+                    "[...{}].sort((a, b) => a < b ? -1 : a > b ? 1 : 0)",
+                    list
+                ))
+            }
+            "sortBy" => {
+                let list = self.emit_expr(&args[0])?;
+                let func = self.emit_expr(&args[1])?;
+                Ok(format!("[...{}].sort({})", list, func))
+            }
             _ => Err(JsGenError {
                 message: format!("Unknown List operation: {}", operation),
                 span: None,