JSON API: Cache-Control no-cache + ETag/304 revalidation

New JsonCacheHeaders middleware (outer, frontend stack): GET/HEAD 200 responses under /_json get a single Cache-Control: no-cache, Expires: 0 and a content md5 ETag; If-None-Match answers as empty 304. Logged-in visitors (fe_typo_user) keep TYPO3 headers. Expires: 0 is deliberate so mod_expires leaves the response alone. .htaccess: the global Header unset ETag now skips /_json (KEEP_ETAG env, carried across the mod_rewrite internal redirect as REDIRECT_KEEP_ETAG). Fulfils tickets 0011-FE point 3 and 0055-BE question 6; asset immutable headers were already live.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/vitec/Configuration/RequestMiddlewares.php

@@ -56,6 +56,17 @@ return [
                 'typo3/cms-core/normalized-params-attribute',
             ],
         ],
+        // Outer response filter: Cache-Control: no-cache + ETag/304 for
+        // /_json (tickets 0011-FE / 0055-BE).
+        'vitec/json-cache-headers' => [
+            'target' => \Evomedien\Vitec\Middleware\JsonCacheHeaders::class,
+            'after' => [
+                'typo3/cms-core/normalized-params-attribute',
+            ],
+            'before' => [
+                'vitec/json-prefix-rewrite',
+            ],
+        ],
     ],
     'backend' => [
         'vitec/sync-ssr-flag' => [