chore: standardize configuration, logging, and error handling across blockchain node and coordinator API

- Add infrastructure.md and workflow files to .gitignore to prevent sensitive info leaks
- Change blockchain node mempool backend default from memory to database for persistence
- Refactor blockchain node logger with StructuredLogFormatter and AuditLogger (consistent with coordinator)
- Add structured logging fields: service, module, function, line number
- Unify coordinator config with Database

docs/5_reference/2_payment-architecture.md

@@ -0,0 +1,145 @@
+# AITBC Payment Architecture
+
+## Overview
+
+The AITBC platform uses a dual-currency system:
+- **AITBC Tokens**: For job payments and platform operations
+- **Bitcoin**: For purchasing AITBC tokens through the exchange
+
+## Payment Flow
+
+### 1. Job Payments (AITBC Tokens)
+```
+Client ──► Creates Job with AITBC Payment ──► Coordinator API
+    │                                        │
+    │                                        ▼
+    │                                  Create Token Escrow
+    │                                        │
+    │                                        ▼
+    │                                  Exchange API (Token)
+    │                                        │
+    ▼                                        ▼
+Miner completes job ──► Release AITBC Escrow ──► Miner Wallet
+```
+
+### 2. Token Purchase (Bitcoin → AITBC)
+```
+Client ──► Bitcoin Payment ──► Exchange API
+    │                           │
+    │                           ▼
+    │                     Process Bitcoin
+    │                           │
+    ▼                           ▼
+Receive AITBC Tokens ◄─── Exchange Rate ◄─── 1 BTC = 100,000 AITBC
+```
+
+## Implementation Details
+
+### Job Payment Structure
+```json
+{
+    "payload": {...},
+    "ttl_seconds": 900,
+    "payment_amount": 100,      // AITBC tokens
+    "payment_currency": "AITBC" // Always AITBC for jobs
+}
+```
+
+### Payment Methods
+- `aitbc_token`: Default for all job payments
+- `bitcoin`: Only used for exchange purchases
+
+### Escrow System
+- **AITBC Token Escrow**: Managed by Exchange API
+  - Endpoint: `/api/v1/token/escrow/create`
+  - Timeout: 1 hour default
+  - Release on job completion
+  
+- **Bitcoin Escrow**: Managed by Wallet Daemon
+  - Endpoint: `/api/v1/escrow/create`
+  - Only for token purchases
+
+## API Endpoints
+
+### Job Payment Endpoints
+- `POST /v1/jobs` - Create job with AITBC payment
+- `GET /v1/jobs/{id}/payment` - Get job payment status
+- `POST /v1/payments/{id}/release` - Release AITBC payment
+- `POST /v1/payments/{id}/refund` - Refund AITBC tokens
+
+### Exchange Endpoints
+- `POST /api/exchange/purchase` - Buy AITBC with BTC
+- `GET /api/exchange/rate` - Get current rate (1 BTC = 100,000 AITBC)
+
+## Database Schema
+
+### Job Payments Table
+```sql
+CREATE TABLE job_payments (
+    id VARCHAR(255) PRIMARY KEY,
+    job_id VARCHAR(255) NOT NULL,
+    amount DECIMAL(20, 8) NOT NULL,
+    currency VARCHAR(10) DEFAULT 'AITBC',
+    payment_method VARCHAR(20) DEFAULT 'aitbc_token',
+    status VARCHAR(20) DEFAULT 'pending',
+    ...
+);
+```
+
+## Security Considerations
+
+1. **Token Validation**: All AITBC payments require valid token balance
+2. **Escrow Security**: Tokens held in smart contract escrow
+3. **Rate Limiting**: Exchange purchases limited per user
+4. **Audit Trail**: All transactions recorded on blockchain
+
+## Example Flow
+
+### 1. Client Creates Job
+```bash
+curl -X POST http://localhost:18000/v1/jobs \
+  -H "X-Api-Key: ${CLIENT_API_KEY}" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "payload": {
+      "job_type": "ai_inference",
+      "parameters": {"model": "gpt-4"}
+    },
+    "payment_amount": 100,
+    "payment_currency": "AITBC"
+  }'
+```
+
+### 2. Response with Payment
+```json
+{
+    "job_id": "abc123",
+    "state": "queued",
+    "payment_id": "pay456",
+    "payment_status": "escrowed",
+    "payment_currency": "AITBC"
+}
+```
+
+### 3. Job Completion & Payment Release
+```bash
+curl -X POST http://localhost:18000/v1/payments/pay456/release \
+  -H "X-Api-Key: ${CLIENT_API_KEY}" \
+  -d '{"job_id": "abc123", "reason": "Job completed"}'
+```
+
+## Benefits
+
+1. **Stable Pricing**: AITBC tokens provide stable job pricing
+2. **Fast Transactions**: Token payments faster than Bitcoin
+3. **Gas Optimization**: Batch operations reduce costs
+4. **Platform Control**: Token supply managed by platform
+
+## Migration Path
+
+1. **Phase 1**: Implement AITBC token payments for new jobs
+2. **Phase 2**: Migrate existing Bitcoin job payments to tokens
+3. **Phase 3**: Phase out Bitcoin for direct job payments
+4. **Phase 4**: Bitcoin only used for token purchases
+
+This architecture ensures efficient job payments while maintaining Bitcoin as the entry point for platform participation.