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/3_miners/5_gpu-setup.md

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+# GPU Setup & Configuration
+Configure and optimize your GPU setup for mining.
+
+## Prerequisites
+
+### Driver Installation
+
+```bash
+# Ubuntu/Debian
+sudo apt install nvidia-driver-535
+
+# Verify installation
+nvidia-smi
+```
+
+### CUDA Installation
+
+```bash
+# Download CUDA from NVIDIA
+wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2204/x86_64/cuda-keyring_1.1-1_all.deb
+sudo dpkg -i cuda-keyring_1.1-1_all.deb
+sudo apt-get update
+sudo apt-get install cuda-toolkit-12-3
+```
+
+## Configuration
+
+### Miner Config
+
+Create `~/.aitbc/miner.yaml`:
+
+```yaml
+gpu:
+  type: v100
+  count: 1
+  cuda_devices: 0
+  
+performance:
+  max_memory_percent: 90
+  max_gpu_temp: 80
+  power_limit: 250
+  
+jobs:
+  max_concurrent: 4
+  timeout_grace: 300
+```
+
+### Environment Variables
+
+```bash
+export CUDA_VISIBLE_DEVICES=0
+export NVIDIA_VISIBLE_DEVICES=all
+export AITBC_GPU_MEMORY_LIMIT=0.9
+```
+
+## Optimization
+
+### Memory Settings
+
+```yaml
+performance:
+  tensor_cores: true
+  fp16: true  # Use half precision
+  max_memory_percent: 90
+```
+
+### Thermal Management
+
+```yaml
+thermal:
+  target_temp: 70
+  max_temp: 85
+  fan_curve:
+    - temp: 50
+      fan: 30
+    - temp: 70
+      fan: 60
+    - temp: 85
+      fan: 100
+```
+
+## Troubleshooting
+
+### GPU Not Detected
+
+```bash
+# Check driver
+nvidia-smi
+
+# Check CUDA
+nvcc --version
+
+# Restart miner
+aitbc miner restart
+```
+
+### Temperature Issues
+
+```bash
+# Monitor temperature
+nvidia-smi -l 1
+
+# Check cooling
+ipmitool sdr list | grep Temp
+```
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Monitoring](./6_monitoring.md) - Monitor your miner
+- [Job Management](./3_job-management.md) — Job management