Add folder anatomy (scripts/agent.py + references/api-reference.md) for 648 cybersecurity skills

Complete skill folder anatomy across all cybersecurity skills:
- scripts/agent.py: 80-150 line Python agents using real libraries (impacket,
  boto3, azure-mgmt-*, kubernetes, pefile, yara, scapy, shodan, stix2, etc.)
- references/api-reference.md: real API documentation with method signatures
- LICENSE: MIT license for all skill folders

skills/detecting-dnp3-protocol-anomalies/references/api-reference.md

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+# API Reference: Detecting DNP3 Protocol Anomalies
+
+## DNP3 Function Codes
+
+| Code | Name | Risk Level |
+|------|------|------------|
+| 0x01 | READ | Normal |
+| 0x02 | WRITE | Caution |
+| 0x03 | SELECT | Caution |
+| 0x04 | OPERATE | Critical |
+| 0x05 | DIRECT_OPERATE | Critical |
+| 0x0D | COLD_RESTART | Critical |
+| 0x0E | WARM_RESTART | Critical |
+| 0x10 | INITIALIZE_APPLICATION | Critical |
+| 0x12 | STOP_APPLICATION | Critical |
+
+## Zeek DNP3 Log Fields
+
+```
+#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p fc_request fc_reply
+```
+
+## Zeek DNP3 Protocol Analyzer
+
+```bash
+# Enable DNP3 analyzer in Zeek
+zeek -C -r capture.pcap protocols/dnp3
+
+# Output: dnp3.log with function codes, objects, IIN bits
+```
+
+## Suricata DNP3 Rules
+
+```
+alert dnp3 any any -> any 20000 (msg:"DNP3 Cold Restart"; \
+  dnp3_func:cold_restart; sid:1000001; rev:1;)
+
+alert dnp3 any any -> any 20000 (msg:"DNP3 Direct Operate"; \
+  dnp3_func:direct_operate; sid:1000002; rev:1;)
+```
+
+## Scapy DNP3 Parsing
+
+```python
+from scapy.all import rdpcap
+from scapy.contrib.dnp3 import DNP3
+
+packets = rdpcap("dnp3_capture.pcap")
+for pkt in packets:
+    if pkt.haslayer(DNP3):
+        print(pkt[DNP3].func_code)
+```
+
+## ICS-CERT Detection Indicators
+
+| Anomaly | Detection Method |
+|---------|-----------------|
+| Unauthorized master | Source IP not in allowed list |
+| Burst traffic | >10 events/sec from single source |
+| Off-hours commands | Control operations outside maintenance windows |
+| Unknown function codes | Function codes not in normal baseline |
+
+## CLI Usage
+
+```bash
+python agent.py --zeek-log dnp3.log
+python agent.py --zeek-log dnp3.log --authorized-masters masters.txt
+```