feat: caption-ninja recipe (web pages, private relay, Caption Local STT)

Self-hosted live captioning from steveseguin/captionninja and
steveseguin/caption-local. Upstream publishes no images, so images/build.sh
builds them from pinned commits.

nginx.conf

@@ -0,0 +1,15 @@
+server {
+    listen       80;
+    listen  [::]:80;
+    server_name  _;
+    root   /usr/share/nginx/html;
+    index  index.html;
+
+    # caption.ninja links omit the extension (e.g. /overlay?room=...).
+    location / {
+        try_files $uri $uri.html $uri/ =404;
+    }
+
+    # Room tokens can arrive in query strings on some pages; keep them out of logs.
+    access_log off;
+}