Add Rust server

Owns the database, PIN rotation and all LiveKit token minting. Kiosk
registration, session-stable joins, admin auth, layouts, branding, media
uploads and the hosted installer script.

server/Dockerfile

@@ -0,0 +1,17 @@
+FROM rust:1-bookworm AS builder
+WORKDIR /build
+COPY server/Cargo.toml ./Cargo.toml
+COPY server/src ./src
+COPY server/assets ./assets
+COPY server/migrations ./migrations
+RUN cargo build --release
+
+FROM debian:bookworm-slim
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+WORKDIR /app
+COPY --from=builder /build/target/release/pistation-server /usr/local/bin/pistation-server
+RUN mkdir -p /data
+EXPOSE 8080
+CMD ["pistation-server"]