Add pi3b hardware tier and resource guards for condo Pi deployment

- Add pi3b tier (700MB RAM limit, 8 passive/2 active modules, no bettercap/mitmproxy)
- Update detect_hardware_tier() to detect Raspberry Pi 3B by model string and BCM2837
- Add pi3b section to hardware_tiers.yaml
- Add systemd MemoryMax/CPUQuota/OOMScoreAdj to all three service files
- Fix bigbrother-watchdog.service ExecStart (was calling non-existent ResourceMonitor().run())
- Add scripts/run_watchdog.py as standalone health monitor daemon

services/bigbrother-watchdog.service

@@ -5,13 +5,16 @@ Requires=bigbrother-core.service
 
 [Service]
 Type=simple
-ExecStart=/opt/.cache/bb/.venv/bin/python3 -c "from core.resource_monitor import ResourceMonitor; ResourceMonitor().run()"
+ExecStart=/opt/.cache/bb/.venv/bin/python3 /opt/.cache/bb/scripts/run_watchdog.py
 WorkingDirectory=/opt/.cache/bb
 Restart=always
 RestartSec=30
 User=root
 StandardOutput=null
 StandardError=null
+MemoryMax=64M
+CPUQuota=25%
+OOMScoreAdj=400
 
 [Install]
 WantedBy=multi-user.target