chore: CLAUDE.md compliance — relative paths, CORS, README tech stack, .vch-description

- Fix absolute API paths in index.html (/analyze, /move, /preview → relative)
- Allow all CORS origins in server.py for reverse-proxy compatibility
- Add tech stack section to README.md
- Create .vch-description for VCH Showcase

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.py

@@ -19,7 +19,7 @@ app = FastAPI(title="Foto-Kurator")
 
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["http://localhost:8000"],
+    allow_origins=["*"],
     allow_methods=["GET", "POST"],
     allow_headers=["Content-Type"],
 )