feat(security): harden gateway boundaries and usage policies

Consolidate subscription usage policy enforcement, privacy-safe persistence, and gateway security hardening into one reviewable change.

Includes bounded HTTP and execution envelopes, header and protocol guards, DNS and relay validation, authentication and secret projection hardening, secure backup/install paths, and regression coverage.

apps/aether-gateway/src/state/bootstrap_admin.rs

@@ -7,13 +7,24 @@ const BOOTSTRAP_ADMIN_EMAIL_ENVS: &[&str] = &["ADMIN_EMAIL"];
 const BOOTSTRAP_ADMIN_USERNAME_ENVS: &[&str] = &["ADMIN_USERNAME"];
 const BOOTSTRAP_ADMIN_PASSWORD_ENVS: &[&str] = &["ADMIN_PASSWORD"];
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Clone, PartialEq, Eq)]
 struct BootstrapAdminConfig {
     email: Option<String>,
     username: String,
     password: String,
 }
 
+impl std::fmt::Debug for BootstrapAdminConfig {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        formatter
+            .debug_struct("BootstrapAdminConfig")
+            .field("email", &self.email)
+            .field("username", &self.username)
+            .field("password", &"[REDACTED]")
+            .finish()
+    }
+}
+
 impl BootstrapAdminConfig {
     fn from_env() -> Result<Option<Self>, GatewayError> {
         Self::from_lookup(|key| {
@@ -495,6 +506,14 @@ mod tests {
         );
     }
 
+    #[test]
+    fn bootstrap_admin_config_debug_output_redacts_password() {
+        let config = bootstrap_config();
+        let debug = format!("{config:?}");
+        assert!(debug.contains("[REDACTED]"));
+        assert!(!debug.contains("Secret123!"));
+    }
+
     #[test]
     fn bootstrap_admin_config_rejects_partial_env() {
         let vars =