fix: cross-compilation musl pour release multi-arch

- rumqttc : use-native-tls → use-rustls (supprime dépendance OpenSSL)
- .cargo/config.toml (racine) : linkers musl + CC/AR pour ring aarch64
- deploy/release.sh : passe CC_aarch64_unknown_linux_musl au build
- .gitignore : règle config.toml affinée (exclut cargo configs)

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

agent/Cargo.toml

@@ -22,7 +22,7 @@ sysinfo = { version = "0.30", default-features = false }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 toml = "0.8"
-rumqttc = { version = "0.24", default-features = false, features = ["use-native-tls"] }
+rumqttc = { version = "0.24", default-features = false, features = ["use-rustls"] }
 
 [dev-dependencies]
 tempfile = "3"