feat: Add systemd service files for HBlink4 and dashboard

- Add hblink4.service for main DMR server
- Add hblink4-dash.service for web dashboard
- Dashboard service depends on main service
- Both use venv at /home/cort/hblink4/venv
- Auto-restart on failure with 10s delay
- Include security hardening (NoNewPrivileges, PrivateTmp)
- Log to systemd journal
- Add SYSTEMD.md with installation and management instructions

SYSTEMD.md

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+# HBlink4 Systemd Service Installation
+
+This directory contains systemd service files for running HBlink4 and its dashboard as system services.
+
+## Service Files
+
+- `hblink4.service` - Main HBlink4 DMR server
+- `hblink4-dash.service` - Web dashboard (depends on hblink4.service)
+
+## Installation
+
+### 1. Install the service files
+
+Copy the service files to systemd's system directory:
+
+```bash
+sudo cp hblink4.service /etc/systemd/system/
+sudo cp hblink4-dash.service /etc/systemd/system/
+```
+
+### 2. Reload systemd
+
+Tell systemd to reload its configuration:
+
+```bash
+sudo systemctl daemon-reload
+```
+
+### 3. Enable services (optional)
+
+To start the services automatically at boot:
+
+```bash
+sudo systemctl enable hblink4
+sudo systemctl enable hblink4-dash
+```
+
+### 4. Start the services
+
+```bash
+sudo systemctl start hblink4
+sudo systemctl start hblink4-dash
+```
+
+## Service Management
+
+### Check service status
+
+```bash
+sudo systemctl status hblink4
+sudo systemctl status hblink4-dash
+```
+
+### View logs
+
+```bash
+# View logs for HBlink4
+sudo journalctl -u hblink4 -f
+
+# View logs for dashboard
+sudo journalctl -u hblink4-dash -f
+
+# View last 100 lines
+sudo journalctl -u hblink4 -n 100
+```
+
+### Stop services
+
+```bash
+sudo systemctl stop hblink4
+sudo systemctl stop hblink4-dash
+```
+
+### Restart services
+
+```bash
+sudo systemctl restart hblink4
+sudo systemctl restart hblink4-dash
+```
+
+### Disable autostart
+
+```bash
+sudo systemctl disable hblink4
+sudo systemctl disable hblink4-dash
+```
+
+## Configuration
+
+The service files are configured to:
+- Run as user `cort` in group `cort`
+- Use the Python virtual environment at `/home/cort/hblink4/venv`
+- Automatically restart on failure (after 10 seconds)
+- Log to systemd journal (view with `journalctl`)
+- Start after network is available
+- Dashboard starts after and depends on HBlink4
+
+### Customization
+
+If you need to modify the services (different user, paths, etc.), edit the files before copying them:
+
+1. Edit `hblink4.service` and/or `hblink4-dash.service`
+2. Change `User=`, `Group=`, `WorkingDirectory=`, or `ExecStart=` as needed
+3. Copy to `/etc/systemd/system/`
+4. Run `sudo systemctl daemon-reload`
+
+## Security Features
+
+Both services include security hardening:
+- `NoNewPrivileges=true` - Prevents privilege escalation
+- `PrivateTmp=true` - Isolates /tmp directory
+
+## Troubleshooting
+
+### Service won't start
+
+Check the status and logs:
+```bash
+sudo systemctl status hblink4
+sudo journalctl -u hblink4 -n 50
+```
+
+Common issues:
+- Virtual environment not found: Check path in `ExecStart=`
+- Permission errors: Ensure user/group are correct
+- Config file errors: Check HBlink4 configuration files
+- Port conflicts: Another service using the same ports
+
+### Dashboard can't connect to HBlink4
+
+1. Ensure HBlink4 is running: `sudo systemctl status hblink4`
+2. Check dashboard config points to correct socket/host
+3. Check logs: `sudo journalctl -u hblink4-dash -n 50`
+
+## Notes
+
+- The dashboard service has `Wants=hblink4.service`, so it will start after HBlink4
+- Both services have `Restart=always` for automatic recovery
+- Logs are sent to systemd journal, not file-based logging
+- Services run with the same privileges as the `cort` user

hblink4-dash.service

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+[Unit]
+Description=HBlink4 Dashboard
+After=network.target hblink4.service
+Wants=hblink4.service
+
+[Service]
+Type=simple
+User=cort
+Group=cort
+WorkingDirectory=/home/cort/hblink4/dashboard
+ExecStart=/home/cort/hblink4/venv/bin/python /home/cort/hblink4/run_dashboard.py
+Restart=always
+RestartSec=10
+
+# Security hardening
+NoNewPrivileges=true
+PrivateTmp=true
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=hblink4-dash
+
+[Install]
+WantedBy=multi-user.target

hblink4.service

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+[Unit]
+Description=HBlink4 DMR Server
+After=network.target
+
+[Service]
+Type=simple
+User=cort
+Group=cort
+WorkingDirectory=/home/cort/hblink4
+ExecStart=/home/cort/hblink4/venv/bin/python /home/cort/hblink4/run.py
+Restart=always
+RestartSec=10
+
+# Security hardening
+NoNewPrivileges=true
+PrivateTmp=true
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=hblink4
+
+[Install]
+WantedBy=multi-user.target