feat: PWA update strategy with hashed assets and cache control

Move frontend sources to frontend/, build content-hashed assets at deploy,
network-first SW for shell/JS, immutable cache for /assets/, version.json
update banner, and Cache-Control middleware. Docs in docs/PWA-STRATEGY.md.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

@@ -9,9 +9,11 @@ COPY pyproject.toml /app/pyproject.toml
 COPY server /app/server
 RUN pip install --no-cache-dir -U pip && pip install --no-cache-dir .
 
-COPY public /app/public
-COPY meds.yaml messages.yaml /app/
+COPY frontend /app/frontend
 COPY tools /app/tools
+RUN python tools/build_frontend.py
+
+COPY meds.yaml messages.yaml /app/
 
 EXPOSE 8000