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/src/main.rs

@@ -0,0 +1,24 @@
+use axum::{routing::get, Router};
+use tracing::info;
+use tracing_subscriber::EnvFilter;
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::from_default_env())
+        .init();
+
+    let app = Router::new().route("/api/v1/health", get(health));
+
+    let addr = "0.0.0.0:8080";
+    info!("SentinelMesh backend démarré sur {addr}");
+
+    let listener = tokio::net::TcpListener::bind(addr).await?;
+    axum::serve(listener, app).await?;
+
+    Ok(())
+}
+
+async fn health() -> &'static str {
+    "ok"
+}