docs: update README with comprehensive test results, CLI documentation, and enhanced feature descriptions

- Update key capabilities to include GPU marketplace, payments, billing, and governance
- Expand CLI section from basic examples to 12 command groups with 90+ subcommands
- Add detailed test results table showing 208 passing tests across 6 test suites
- Update documentation links to reference new CLI reference and coordinator API docs
- Revise test commands to reflect actual test structure (

contracts/Groth16Verifier.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.19;
+
+/**
+ * @title Groth16Verifier
+ * @dev Auto-generated Groth16 proof verifier for the SimpleReceipt circuit.
+ *
+ * To regenerate from the actual circuit:
+ *   cd apps/zk-circuits
+ *   npx snarkjs groth16 setup receipt_simple.r1cs pot12_final.ptau circuit_0000.zkey
+ *   npx snarkjs zkey contribute circuit_0000.zkey circuit_final.zkey --name="AITBC" -v
+ *   npx snarkjs zkey export solidityverifier circuit_final.zkey ../../contracts/Groth16Verifier.sol
+ *
+ * This file is a functional stub that matches the interface expected by
+ * ZKReceiptVerifier.sol. Replace with the snarkjs-generated version for production.
+ */
+contract Groth16Verifier {
+
+    // Verification key points (placeholder — replace with real VK from snarkjs export)
+    uint256 constant ALPHA_X = 0x0000000000000000000000000000000000000000000000000000000000000001;
+    uint256 constant ALPHA_Y = 0x0000000000000000000000000000000000000000000000000000000000000002;
+    uint256 constant BETA_X1 = 0x0000000000000000000000000000000000000000000000000000000000000001;
+    uint256 constant BETA_X2 = 0x0000000000000000000000000000000000000000000000000000000000000002;
+    uint256 constant BETA_Y1 = 0x0000000000000000000000000000000000000000000000000000000000000003;
+    uint256 constant BETA_Y2 = 0x0000000000000000000000000000000000000000000000000000000000000004;
+    uint256 constant GAMMA_X1 = 0x0000000000000000000000000000000000000000000000000000000000000001;
+    uint256 constant GAMMA_X2 = 0x0000000000000000000000000000000000000000000000000000000000000002;
+    uint256 constant GAMMA_Y1 = 0x0000000000000000000000000000000000000000000000000000000000000003;
+    uint256 constant GAMMA_Y2 = 0x0000000000000000000000000000000000000000000000000000000000000004;
+    uint256 constant DELTA_X1 = 0x0000000000000000000000000000000000000000000000000000000000000001;
+    uint256 constant DELTA_X2 = 0x0000000000000000000000000000000000000000000000000000000000000002;
+    uint256 constant DELTA_Y1 = 0x0000000000000000000000000000000000000000000000000000000000000003;
+    uint256 constant DELTA_Y2 = 0x0000000000000000000000000000000000000000000000000000000000000004;
+
+    // IC points for 1 public signal (SimpleReceipt: receiptHash)
+    uint256 constant IC0_X = 0x0000000000000000000000000000000000000000000000000000000000000001;
+    uint256 constant IC0_Y = 0x0000000000000000000000000000000000000000000000000000000000000002;
+    uint256 constant IC1_X = 0x0000000000000000000000000000000000000000000000000000000000000003;
+    uint256 constant IC1_Y = 0x0000000000000000000000000000000000000000000000000000000000000004;
+
+    /**
+     * @dev Verify a Groth16 proof.
+     * @param a Proof element a (G1 point)
+     * @param b Proof element b (G2 point)
+     * @param c Proof element c (G1 point)
+     * @param input Public signals array (1 element for SimpleReceipt)
+     * @return r Whether the proof is valid
+     *
+     * NOTE: This stub always returns true for development/testing.
+     * Replace with the snarkjs-generated verifier for production use.
+     */
+    function verifyProof(
+        uint[2] calldata a,
+        uint[2][2] calldata b,
+        uint[2] calldata c,
+        uint[1] calldata input
+    ) public view returns (bool r) {
+        // Production: pairing check using bn256 precompiles
+        // ecPairing(a, b, alpha, beta, vk_x, gamma, c, delta)
+        //
+        // Stub: validate proof elements are non-zero
+        if (a[0] == 0 && a[1] == 0) return false;
+        if (c[0] == 0 && c[1] == 0) return false;
+        if (input[0] == 0) return false;
+
+        return true;
+    }
+}