Add client download link and build tarball during deployment

- Added /download/client endpoint to serve the CLI client tarball
- Added "Client" link to navigation in base template
- Created build-client.sh script to clone and package the client
- Updated Dockerfile to run build-client.sh during container build

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -16,6 +16,9 @@ COPY . .
 # Clone effects repo
 RUN git clone https://git.rose-ash.com/art-dag/effects.git /app/artdag-effects
 
+# Build client tarball for download
+RUN ./build-client.sh
+
 # Create cache directory
 RUN mkdir -p /data/cache