Force pip cache bust on deploy

- Add CACHEBUST build arg to Dockerfile
- Pass timestamp to --build-arg in deploy.sh
- Ensures artdag is re-fetched from GitHub on each deploy

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

Dockerfile

@@ -7,6 +7,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends git ffmpeg && r
 
 # Install dependencies
 COPY requirements.txt .
+ARG CACHEBUST=1
 RUN pip install --no-cache-dir -r requirements.txt
 
 # Copy application