feat(agent): setup Cargo.toml et structure complète

Initialise la structure de l'agent Rust avec tous les modules stub :
config, payload, metrics (cpu/memory/disk/network/uptime/temperature/smart),
transport (udp/mqtt). Corrige les features sysinfo 0.30 (pas de feature
disk/networks séparées). Compile sans erreurs.

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

agent/Cargo.toml

@@ -18,7 +18,7 @@ lto = true
 codegen-units = 1
 
 [dependencies]
-sysinfo = { version = "0.30", default-features = false, features = ["system", "networks", "disk"] }
+sysinfo = { version = "0.30", default-features = false }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 toml = "0.8"