refactor: simplify LinterResult type

Remove output/report compatibility workaround since type errors with
older stylelint versions are pre-existing and accepted.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: zalishchuk

src/linter.js

@@ -236,13 +236,11 @@ function linter(key, options, compilation) {
 
     const formatter = await loadFormatter(getStylelint, options.formatter);
 
-    // Include both output (v13-v16) and report (v17+) for compatibility
-    /** @type {LinterResult & { output?: string }} */
+    /** @type {LinterResult} */
     const returnValue = {
       cwd: /** @type {string} */ (options.cwd),
       errored: false,
       results: [],
-      output: "",
       report: "",
       reportedDisables: [],
       ruleMetadata: getRuleMetadata(results),