feat: add Docker Compose support for Discord bot deployment

- Add Dockerfile with multi-stage build for picoclaw
- Add docker-compose.discord.yml for Discord bot service
- Add docker-compose.yml for agent mode service
- Add .env.example with environment variable template
- Add .dockerignore for optimized builds
- Update README.md with Docker Compose section and language switch
- Add README.ja.md (Japanese documentation)
- Update .gitignore with Docker-related entries

Dockerfile

@@ -0,0 +1,36 @@
+# ============================================================
+# Stage 1: Build the picoclaw binary
+# ============================================================
+FROM golang:1.24-alpine AS builder
+
+RUN apk add --no-cache git make
+
+WORKDIR /src
+
+# Cache dependencies
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source and build
+COPY . .
+RUN make build
+
+# ============================================================
+# Stage 2: Minimal runtime image
+# ============================================================
+FROM alpine:3.21
+
+RUN apk add --no-cache ca-certificates tzdata
+
+# Copy binary
+COPY --from=builder /src/build/picoclaw /usr/local/bin/picoclaw
+
+# Copy builtin skills
+COPY --from=builder /src/skills /opt/picoclaw/skills
+
+# Create picoclaw home directory
+RUN mkdir -p /root/.picoclaw/workspace/skills && \
+    cp -r /opt/picoclaw/skills/* /root/.picoclaw/workspace/skills/ 2>/dev/null || true
+
+ENTRYPOINT ["picoclaw"]
+CMD ["gateway"]