docs(test): note boundaries/element-types deprecated-alias coupling

Documents that the test filter and the .eslintrc rule key both use the
v5-era 'boundaries/element-types' alias; a future eslint-plugin-boundaries
bump that drops the alias must update both together or the filter silently
matches nothing. Addresses the Task 4 code-review Minor.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/app/tests/unit/boundaries-v2.spec.ts

@@ -14,6 +14,14 @@ const rootDir = path.resolve(__dirname, '../../')
 
 const eslint = new ESLint({ cwd: rootDir })
 
+// Filter on the boundaries/element-types ruleId, which is the deprecated
+// alias for boundaries/dependencies (renamed in eslint-plugin-boundaries
+// v5→v6). The installed 6.0.2 still reports violations under the old
+// ruleId while .eslintrc.cjs's rule key is also 'boundaries/element-types'.
+// If a future bump drops the alias, update this filter AND the eslintrc
+// key together (TECH-WS-GUI-REDESIGN tracks the full migration to
+// 'boundaries/dependencies') — otherwise this filter silently matches
+// nothing and the tests pass even when the rule fires.
 async function boundaryErrors(filePath: string, code: string) {
   const [result] = await eslint.lintText(code, { filePath })