SSR switch-on fix: proxy the DirectoryIndex homepage detour

First switch-on with a running node: Apache mod_dir turns / into /index.html via the DirectoryIndex subrequest before the per-dir root rule can proxy it; the node then asked for /_json/index.html and rendered a cacheable 404 homepage. New flag-gated rule proxies index.html as / to the node. Companion fix outside git: public/_frontend/.htaccess (build output, gitignored) overrides the root rewrites for /_frontend/*, so release assets only existing on the VPS were answered by its SPA fallback with index.html - HTML served as JS; the flag-gated asset proxy now also sits in that file before the fallback, and the frontend build must adopt it in its .htaccess template (ticket 0059-BE).

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

public/_frontend/.htaccess

@@ -3,6 +3,14 @@ RewriteBase /_frontend/
 
 RewriteRule ^index\.html$ - [L]
 
+# SSR flag ON: hashed assets are served from the VPS release - its hashes
+# must win over any local build, and the fallback below must never answer
+# an asset request with index.html (the browser would get HTML as JS).
+# This directory's .htaccess overrides the root one for /_frontend/*, so
+# the rule has to live HERE, not in public/.htaccess (2026-11-09).
+RewriteCond /usr/www/users/vitecevo/live/var/vitec-ssr-on.flag -f
+RewriteRule ^assets/(.*)$ https://vitec-ssr.evomedien.de/_frontend/assets/$1 [P,L]
+
 RewriteCond %{REQUEST_FILENAME} -f [OR]
 RewriteCond %{REQUEST_FILENAME} -d
 RewriteRule ^ - [L]