Add full monorepo: virtual-banker, backend, frontend, docs, scripts, deployment

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/specs/observability/logging.md

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+# Logging Architecture Specification
+
+## Overview
+
+Centralized logging architecture for the explorer platform.
+
+## Log Aggregation Strategy
+
+**Solution**: ELK Stack (Elasticsearch, Logstash, Kibana) or Loki + Grafana
+
+**Flow**:
+1. Services emit logs
+2. Log collectors aggregate logs
+3. Logs stored in central store
+4. Dashboards and queries via UI
+
+## Log Levels and Categorization
+
+### Log Levels
+
+- **DEBUG**: Detailed debugging information
+- **INFO**: General informational messages
+- **WARN**: Warning messages
+- **ERROR**: Error messages
+- **FATAL**: Critical errors
+
+### Categories
+
+**Application Logs**: Business logic, API requests
+**Access Logs**: HTTP requests, authentication
+**System Logs**: Infrastructure, system events
+**Audit Logs**: Security events, compliance
+
+## Structured Logging Format
+
+### Log Format
+
+```json
+{
+  "timestamp": "2024-01-01T00:00:00Z",
+  "level": "INFO",
+  "service": "explorer-api",
+  "message": "Request processed",
+  "request_id": "uuid",
+  "user_id": "uuid",
+  "chain_id": 138,
+  "method": "GET",
+  "path": "/api/v1/blocks",
+  "status_code": 200,
+  "duration_ms": 45,
+  "metadata": {}
+}
+```
+
+## Log Retention Policies
+
+**Development**: 7 days
+**Staging**: 30 days
+**Production**: 90 days (hot), 1 year (cold archive)
+
+## PII Sanitization in Logs
+
+**Strategy**: Remove PII before logging
+**Fields to Sanitize**:
+- Email addresses
+- Personal names
+- Addresses
+- API keys (partial masking)
+
+**Implementation**: Log sanitization middleware
+
+## References
+
+- Metrics & Monitoring: See `metrics-monitoring.md`
+