Add self-hosted RCS backend, extension, and ops tooling

Ship the Go/SQLite API and Web UI, Chrome/Brave capture addon,
Docker Compose, Pangolin reverse-proxy support, and a user-crontab
watchdog so the binary stays running without systemd.

backend/Dockerfile

@@ -0,0 +1,16 @@
+FROM golang:1.24-bookworm AS build
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 go build -o /out/rcs ./cmd/rcs
+
+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=build /out/rcs /app/rcs
+ENV RCS_ADDR=0.0.0.0:8080
+ENV RCS_DATA_DIR=/data
+VOLUME ["/data"]
+EXPOSE 8080
+ENTRYPOINT ["/app/rcs"]