fix(cinny/nginx): let the app frame its bundled Element Call again

Web calls broke ("nobody can join calls from the web version"): 23ad133
(cinny #210) put the security-headers snippet, including the app CSP, on
every .html response. /public/element-call/index.html then carried
frame-ancestors 'none', so the browser refused to load it inside the app
("Content-Security-Policy ... frame-ancestors 'none'"). Desktop was fine (it
loads Element Call from its own bundle). Before #210 that page had no CSP.

A `location ^~ /public/element-call/` now serves it with
cinny-security-headers-framed.conf: the same headers minus the CSP
(X-Frame-Options SAMEORIGIN still limits framing to chat.lotusguild.org),
and the same caching (HTML no-cache, hashed assets 1 year). Applied live on
LXC 106 (backup sites-available/cinny.bak-ecframe-*), nginx -t ok; verified
from outside: no CSP on the call page, and the live site frames it and it
loads ("Element Call").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

cinny/nginx-security-headers-framed.conf

@@ -0,0 +1,11 @@
+# Headers for the bundled Element Call page (/public/element-call/).
+# Same as cinny-security-headers.conf minus the Content-Security-Policy: the app
+# embeds this page in an iframe, and the app CSP's frame-ancestors 'none' (plus a
+# connect-src that doesn't list the call backends) blocked it. X-Frame-Options
+# SAMEORIGIN still limits framing to chat.lotusguild.org itself.
+add_header X-Frame-Options SAMEORIGIN always;
+add_header X-Content-Type-Options nosniff always;
+add_header X-XSS-Protection "1; mode=block" always;
+add_header Referrer-Policy strict-origin-when-cross-origin always;
+add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
+add_header Permissions-Policy "accelerometer=(), autoplay=(self), camera=(self), display-capture=(self), encrypted-media=(self), fullscreen=(self), geolocation=(self), gyroscope=(), magnetometer=(), microphone=(self), midi=(), payment=(), usb=()" always;

cinny/nginx.conf

@@ -51,6 +51,23 @@ server {
         add_header Cache-Control "no-cache, no-store, must-revalidate" always;
     }
 
+    # Bundled Element Call: framed by the app itself, so it must not carry the
+    # app CSP (frame-ancestors 'none' blocked every web call). Same caching as
+    # below: HTML never cached, hashed assets for a year.
+    location ^~ /public/element-call/ {
+        include snippets/cinny-security-headers-framed.conf;
+        location ~* \.html$ {
+            include snippets/cinny-security-headers-framed.conf;
+            expires -1;
+            add_header Cache-Control "no-cache, no-store, must-revalidate" always;
+        }
+        location ~* \.(?:js|css|woff2?|png|svg|ico|webp|wasm)$ {
+            include snippets/cinny-security-headers-framed.conf;
+            expires 1y;
+            add_header Cache-Control "public, immutable" always;
+        }
+    }
+
     # Cache content-addressed static assets aggressively
     location ~* \.(?:js|css|woff2?|png|svg|ico|webp)$ {
         include snippets/cinny-security-headers.conf;