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

docs/user-guide/marketplace.md

@@ -0,0 +1,46 @@
+---
+title: Marketplace
+description: Using the AITBC marketplace
+---
+
+# Marketplace
+
+The AITBC marketplace connects job creators with miners who can execute their AI workloads.
+
+## How It Works
+
+1. **Job Creation**: Users create jobs with specific requirements
+2. **Offer Matching**: The marketplace finds suitable miners
+3. **Execution**: Miners execute the jobs and submit results
+4. **Payment**: Automatic payment upon successful completion
+
+## Finding Services
+
+Browse available services:
+- By job type
+- By price range
+- By miner reputation
+- By resource requirements
+
+## Pricing
+
+Dynamic pricing based on:
+- Market demand
+- Resource availability
+- Miner reputation
+- Job complexity
+
+## Creating Offers
+
+As a miner, you can:
+- Set your prices
+- Specify job types
+- Define resource limits
+- Build reputation
+
+## Safety Features
+
+- Escrow payments
+- Dispute resolution
+- Reputation system
+- Cryptographic proofs