test: add config validation suite (43/43 tests)

Adds 4 regression tests:
- vite.config.ts entry modules must exist as source files
- content.js must NOT use inline script injection (textContent)
- interceptors.js must be a standalone IIFE file
- manifest.json content_scripts must reference content.js

Prevents future build-breaking phantom entry point errors
(the probeFn.js/scrapeFn.js issue kfj001 hit).

__tests__/run.mjs

@@ -5,6 +5,7 @@ import './schema.test.mjs';
 import './viewer_units.test.mjs';
 import './data_flow.test.mjs';
 import './viewer_integration.test.mjs';
+import './config_validation.test.mjs';
 import { run } from './runner.mjs';
 
 const result = await run();