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.

images/web/Dockerfile

@@ -0,0 +1,7 @@
+# Static caption.ninja pages. Build context: a captionninja checkout.
+FROM alpine:3.22 AS src
+COPY . /src
+RUN cd /src && rm -rf .git .github relay scripts *.md test-security-warning.html
+
+FROM nginx:1.31.6-alpine
+COPY --from=src /src /usr/share/nginx/html