feat: add marketplace metrics, privacy features, and service registry endpoints

- Add Prometheus metrics for marketplace API throughput and error rates with new dashboard panels
- Implement confidential transaction models with encryption support and access control
- Add key management system with registration, rotation, and audit logging
- Create services and registry routers for service discovery and management
- Integrate ZK proof generation for privacy-preserving receipts
- Add metrics instru

apps/zk-circuits/receipt.circom

@@ -0,0 +1,125 @@
+pragma circom 2.0.0;
+
+include "circomlib/circuits/bitify.circom";
+include "circomlib/circuits/escalarmulfix.circom";
+include "circomlib/circuits/comparators.circom";
+include "circomlib/circuits/poseidon.circom";
+
+/*
+ * Receipt Attestation Circuit
+ * 
+ * This circuit proves that a receipt is valid without revealing sensitive details.
+ * 
+ * Public Inputs:
+ * - receiptHash: Hash of the receipt (for public verification)
+ * - settlementAmount: Amount to be settled (public)
+ * - timestamp: Receipt timestamp (public)
+ * 
+ * Private Inputs:
+ * - receipt: The full receipt data (private)
+ * - computationResult: Result of the computation (private)
+ * - pricingRate: Pricing rate used (private)
+ * - minerReward: Reward for miner (private)
+ * - coordinatorFee: Fee for coordinator (private)
+ */
+
+template ReceiptAttestation() {
+    // Public signals
+    signal input receiptHash;
+    signal input settlementAmount;
+    signal input timestamp;
+    
+    // Private signals
+    signal input receipt[8];
+    signal input computationResult;
+    signal input pricingRate;
+    signal input minerReward;
+    signal input coordinatorFee;
+    
+    // Components
+    component hasher = Poseidon(8);
+    component amountChecker = GreaterEqThan(8);
+    component feeCalculator = Add8(8);
+    
+    // Hash the receipt to verify it matches the public hash
+    for (var i = 0; i < 8; i++) {
+        hasher.inputs[i] <== receipt[i];
+    }
+    
+    // Ensure the computed hash matches the public hash
+    hasher.out === receiptHash;
+    
+    // Verify settlement amount calculation
+    // settlementAmount = minerReward + coordinatorFee
+    feeCalculator.a[0] <== minerReward;
+    feeCalculator.a[1] <== coordinatorFee;
+    for (var i = 2; i < 8; i++) {
+        feeCalculator.a[i] <== 0;
+    }
+    feeCalculator.out === settlementAmount;
+    
+    // Ensure amounts are non-negative
+    amountChecker.in[0] <== settlementAmount;
+    amountChecker.in[1] <== 0;
+    amountChecker.out === 1;
+    
+    // Additional constraints can be added here:
+    // - Timestamp validation
+    // - Pricing rate bounds
+    // - Computation result format
+}
+
+/*
+ * Simplified Receipt Hash Preimage Circuit
+ * 
+ * This is a minimal circuit for initial testing that proves
+ * knowledge of a receipt preimage without revealing it.
+ */
+template ReceiptHashPreimage() {
+    // Public signal
+    signal input hash;
+    
+    // Private signals (receipt data)
+    signal input data[4];
+    
+    // Hash component
+    component poseidon = Poseidon(4);
+    
+    // Connect inputs
+    for (var i = 0; i < 4; i++) {
+        poseidon.inputs[i] <== data[i];
+    }
+    
+    // Constraint: computed hash must match public hash
+    poseidon.out === hash;
+}
+
+/*
+ * ECDSA Signature Verification Component
+ * 
+ * Verifies that a receipt was signed by the coordinator
+ */
+template ECDSAVerify() {
+    // Public inputs
+    signal input publicKey[2];
+    signal input messageHash;
+    signal input signature[2];
+    
+    // Private inputs
+    signal input r;
+    signal input s;
+    
+    // Note: Full ECDSA verification in circom is complex
+    // This is a placeholder for the actual implementation
+    // In practice, we'd use a more efficient approach like:
+    // - EDDSA verification (simpler in circom)
+    // - Or move signature verification off-chain
+    
+    // Placeholder constraint
+    signature[0] * signature[1] === r * s;
+}
+
+/*
+ * Main circuit for initial implementation
+ */
+component main = ReceiptHashPreimage();