chore: initialise la structure du projet SentinelMesh

- Workspace Cargo avec backend, agent-scan-network, agent-metric
- Skeleton Rust pour les trois crates (Axum, Tokio, SQLx)
- Documentation : README, FEATURES, ROADMAP, ARCHITECTURE, API, INSTALL
- Exemples de widgets Glance (custom-api)
- Script d'installation agents (squelette Phase 5)
- Docker Compose + Dockerfile backend
- .gitignore et CLAUDE.md

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

backend/Dockerfile

@@ -0,0 +1,13 @@
+FROM rust:1.82-alpine AS builder
+RUN apk add --no-cache musl-dev
+WORKDIR /app
+COPY Cargo.toml Cargo.lock* ./
+COPY src ./src
+RUN cargo build --release
+
+FROM alpine:3.21
+RUN apk add --no-cache ca-certificates
+WORKDIR /app
+COPY --from=builder /app/target/release/sentinelmesh-backend .
+EXPOSE 8080
+CMD ["./sentinelmesh-backend"]