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/control/auth/gate.rs

@@ -224,7 +224,7 @@ fn wallet_finite_available_usd(
     Some(wallet.balance.max(0.0) + wallet.gift_balance.max(0.0))
 }
 
-async fn estimate_execution_plan_cost_upper_bound_usd(
+pub(crate) async fn estimate_execution_plan_cost_upper_bound_usd(
     state: &AppState,
     plan: &aether_contracts::ExecutionPlan,
     report_context: Option<&serde_json::Value>,
@@ -925,6 +925,7 @@ mod tests {
             local_rejection: None,
             allowed_models: Some(allowed_models),
             ip_rules: None,
+            verified_api_key_hash: None,
         });
         decision
     }