feat(docker): Dockerfiles agents multi-arch (amd64, arm64, armv7)

- Build en 2 étapes : rust:1.82-alpine → alpine:3.21
- Mapping automatique TARGETPLATFORM → target musl Rust
- Cache couche dépendances Cargo (builds incrémentaux rapides)
- agent-scan-network : inclut iputils (ping)
- agent-metric : inclut smartmontools (SMART), requiert --privileged pour /sys

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents/agent-metric/Dockerfile

@@ -0,0 +1,36 @@
+# Build multi-arch : docker buildx build --platform linux/amd64,linux/arm64 .
+# Note : agent-metric nécessite accès /sys et /proc — lancer avec --privileged
+FROM --platform=$BUILDPLATFORM rust:1.82-alpine AS builder
+
+ARG TARGETPLATFORM
+
+RUN apk add --no-cache musl-dev
+
+RUN case "$TARGETPLATFORM" in \
+    "linux/amd64")   echo "x86_64-unknown-linux-musl"    > /rust_target ;; \
+    "linux/arm64")   echo "aarch64-unknown-linux-musl"   > /rust_target ;; \
+    "linux/arm/v7")  echo "armv7-unknown-linux-musleabihf" > /rust_target ;; \
+    *) echo "x86_64-unknown-linux-musl" > /rust_target ;; \
+    esac
+
+RUN rustup target add "$(cat /rust_target)"
+
+WORKDIR /build
+
+COPY Cargo.toml ./
+RUN mkdir src && echo 'fn main(){}' > src/main.rs
+RUN cargo build --release --target "$(cat /rust_target)" 2>/dev/null || true
+RUN rm -rf src
+
+COPY src ./src
+RUN cargo build --release --target "$(cat /rust_target)"
+RUN cp "target/$(cat /rust_target)/release/agent-metric" /agent
+
+FROM alpine:3.21
+RUN apk add --no-cache ca-certificates smartmontools
+WORKDIR /app
+COPY --from=builder /agent ./agent-metric
+EXPOSE 9101
+VOLUME ["/app/config.yaml"]
+# Accès /sys /proc /dev nécessaire pour les métriques — docker run --privileged
+ENTRYPOINT ["./agent-metric", "/app/config.yaml"]