Add self-hosted PocketBase stack with auto-migrations

- docker-compose.yml: app + pocketbase services (PB internal to the network)
- pocketbase/: pinned PocketBase image, superuser bootstrap via env vars
- pb_migrations: production schema (collections, rules, public_users view)
  applied automatically on first boot
- pocketbase/pb_schema.json: schema export kept as reference
- README: full-stack deployment docs

pocketbase/Dockerfile

@@ -0,0 +1,19 @@
+# PocketBase backend with auto-applied migrations (collections + rules).
+# Migrations in ./pb_migrations run automatically when the server starts.
+FROM alpine:3.21
+
+ARG PB_VERSION=0.39.9
+
+RUN apk add --no-cache ca-certificates curl unzip
+
+WORKDIR /pb
+RUN curl -fsSL "https://github.com/pocketbase/pocketbase/releases/download/v${PB_VERSION}/pocketbase_${PB_VERSION}_linux_amd64.zip" -o pb.zip \
+    && unzip pb.zip \
+    && rm pb.zip
+
+COPY pb_migrations ./pb_migrations
+COPY entrypoint.sh ./
+RUN chmod +x entrypoint.sh pocketbase
+
+EXPOSE 8090
+CMD ["./entrypoint.sh"]