Add Docker support: Dockerfile, docker-compose.yaml, and README updates

Dockerfile

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+# syntax=docker/dockerfile:1
+
+FROM golang:1.23-alpine AS builder
+WORKDIR /src
+
+# Pull modules first for better layer cache.
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /out/laodingbot ./cmd/bot
+
+FROM alpine:3.20
+WORKDIR /app
+
+RUN apk add --no-cache ca-certificates tzdata
+
+COPY --from=builder /out/laodingbot /app/laodingbot
+
+# Keep default runtime assets in image; can be overridden by bind mounts.
+COPY bot_context /app/bot_context
+COPY skills /app/skills
+COPY workspace/agent_runtime /app/workspace/agent_runtime
+
+ENV MESSAGE_CHANNEL=webui
+ENV WEBUI_LISTEN_ADDR=:8090
+ENV AGENT_WORKSPACE_DIR=/app/workspace/agent_runtime
+
+# Host can bind mount these directories for persistent/external runtime data.
+VOLUME ["/app/workspace/agent_runtime"]
+
+EXPOSE 8090
+
+CMD ["/app/laodingbot"]