Move blockchain app READMEs to centralized documentation

- Relocate blockchain-event-bridge README content to docs/apps/blockchain/blockchain-event-bridge.md
- Relocate blockchain-explorer README content to docs/apps/blockchain/blockchain-explorer.md
- Replace app READMEs with redirect notices pointing to new documentation location
- Consolidate documentation in central docs/ directory for better organization

docs/apps/marketplace/pool-hub.md

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+# Pool Hub
+
+## Purpose & Scope
+
+Matchmaking gateway between coordinator job requests and available miners. See `docs/bootstrap/pool_hub.md` for architectural guidance.
+
+## Development Setup
+
+- Create a Python virtual environment under `apps/pool-hub/.venv`.
+- Install FastAPI, Redis (optional), and PostgreSQL client dependencies once requirements are defined.
+- Implement routers and registry as described in the bootstrap document.
+
+## SLA Monitoring and Billing Integration
+
+Pool-Hub now includes comprehensive SLA monitoring and billing integration with coordinator-api:
+
+### SLA Metrics
+
+- **Miner Uptime**: Tracks miner availability based on heartbeat intervals
+- **Response Time**: Monitors average response time from match results
+- **Job Completion Rate**: Tracks successful vs failed job outcomes
+- **Capacity Availability**: Monitors overall pool capacity utilization
+
+### SLA Thresholds
+
+Default thresholds (configurable in settings):
+- Uptime: 95%
+- Response Time: 1000ms
+- Completion Rate: 90%
+- Capacity Availability: 80%
+
+### Billing Integration
+
+Pool-Hub integrates with coordinator-api's billing system to:
+- Record usage data (gpu_hours, api_calls, compute_hours)
+- Sync miner usage to tenant billing
+- Generate invoices via coordinator-api
+- Track billing metrics and costs
+
+### API Endpoints
+
+SLA and billing endpoints are available under `/sla/`:
+- `GET /sla/metrics/{miner_id}` - Get SLA metrics for a miner
+- `GET /sla/metrics` - Get SLA metrics across all miners
+- `GET /sla/violations` - Get SLA violations
+- `POST /sla/metrics/collect` - Trigger SLA metrics collection
+- `GET /sla/capacity/snapshots` - Get capacity planning snapshots
+- `GET /sla/capacity/forecast` - Get capacity forecast
+- `GET /sla/capacity/recommendations` - Get scaling recommendations
+- `GET /sla/billing/usage` - Get billing usage data
+- `POST /sla/billing/sync` - Trigger billing sync with coordinator-api
+
+### Configuration
+
+Add to `.env`:
+```bash
+# Coordinator-API Billing Integration
+COORDINATOR_BILLING_URL=http://localhost:8011
+COORDINATOR_API_KEY=your_api_key_here
+
+# SLA Configuration
+SLA_UPTIME_THRESHOLD=95.0
+SLA_RESPONSE_TIME_THRESHOLD=1000.0
+SLA_COMPLETION_RATE_THRESHOLD=90.0
+SLA_CAPACITY_THRESHOLD=80.0
+
+# Capacity Planning
+CAPACITY_FORECAST_HOURS=168
+CAPACITY_ALERT_THRESHOLD_PCT=80.0
+
+# Billing Sync
+BILLING_SYNC_INTERVAL_HOURS=1
+
+# SLA Collection
+SLA_COLLECTION_INTERVAL_SECONDS=300
+```
+
+### Database Migration
+
+Run the database migration to add SLA and capacity tables:
+```bash
+cd apps/pool-hub
+alembic upgrade head
+```
+
+### Testing
+
+Run tests for SLA and billing integration:
+```bash
+cd apps/pool-hub
+pytest tests/test_sla_collector.py
+pytest tests/test_billing_integration.py
+pytest tests/test_sla_endpoints.py
+pytest tests/test_integration_coordinator.py
+```