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

core/engine.py

@@ -37,6 +37,14 @@ HARDWARE_TIERS = {
         "allow_mitmproxy": True,
         "allow_bettercap": True,
     },
+    "pi3b": {
+        "max_passive": 8,
+        "max_active": 2,
+        "max_ram_mb": 700,  # 900MB total - ~200MB OS overhead
+        "max_cpu_pct": 75,
+        "allow_mitmproxy": False,
+        "allow_bettercap": False,
+    },
     "pi_zero": {
         "max_passive": 4,
         "max_active": 0,
@@ -78,9 +86,16 @@ def detect_hardware_tier() -> str:
     if "allwinner" in cpuinfo and "h618" in cpuinfo:
         return "opi_zero3"
 
-    if "raspberry pi zero 2" in model or "bcm2710" in cpuinfo:
+    if "raspberry pi zero 2" in model:
         return "pi_zero"
 
+    if "raspberry pi 3" in model:
+        return "pi3b"
+
+    # BCM2710/BCM2837 without a clear model string — Pi 3B family
+    if "bcm2837" in cpuinfo or ("bcm2710" in cpuinfo and "raspberry pi zero 2" not in model):
+        return "pi3b"
+
     return "generic"