fix(tests): update 5 source-text tests to read config-schema.cjs (#2480)

VALID_CONFIG_KEYS moved from config.cjs to config-schema.cjs in the
drift-prevention companion PR. Tests that read config.cjs source text
and checked for key literal includes() now point to the correct file.

Closes #2480

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/thinking-partner.test.cjs

@@ -68,7 +68,7 @@ describe('Thinking Partner Integration (#1726)', () => {
   describe('Config integration', () => {
     test('features.thinking_partner is in VALID_CONFIG_KEYS', () => {
       const configSrc = fs.readFileSync(
-        path.join(GSD_ROOT, 'bin', 'lib', 'config.cjs'),
+        path.join(GSD_ROOT, 'bin', 'lib', 'config-schema.cjs'),
         'utf-8'
       );
       assert.ok(