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/performing-subdomain-enumeration-with-subfinder/references/api-reference.md

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+# API Reference: Subdomain Enumeration with Subfinder
+
+## Subfinder CLI Options
+
+| Flag | Description |
+|------|-------------|
+| `-d <domain>` | Target domain to enumerate |
+| `-dL <file>` | File containing list of domains |
+| `-o <file>` | Output file for results |
+| `-oJ` | JSON lines output format |
+| `-oD <dir>` | Output directory (one file per domain) |
+| `-all` | Use all passive sources (slower, more thorough) |
+| `-silent` | Show only subdomains in output |
+| `-recursive` | Enumerate subdomains of discovered subdomains |
+| `-s <src1,src2>` | Use only specified sources |
+| `-es <src>` | Exclude specific sources |
+| `-cs` | Show source for each subdomain |
+| `-rate-limit <n>` | Max requests per second |
+| `-t <n>` | Number of concurrent threads |
+
+## httpx CLI Options
+
+| Flag | Description |
+|------|-------------|
+| `-l <file>` | Input file with hosts |
+| `-ports <p1,p2>` | Ports to probe |
+| `-status-code` | Show HTTP status code |
+| `-title` | Show page title |
+| `-tech-detect` | Detect web technologies |
+| `-json` | JSON output format |
+| `-silent` | Suppress banner |
+
+## dnsx CLI Options
+
+| Flag | Description |
+|------|-------------|
+| `-l <file>` | Input file with hosts |
+| `-a` | Resolve A records |
+| `-cname` | Resolve CNAME records |
+| `-resp` | Show response data |
+| `-json` | JSON output |
+
+## Passive Sources
+
+| Source | API Key Required |
+|--------|-----------------|
+| crt.sh | No |
+| VirusTotal | Yes |
+| Shodan | Yes |
+| SecurityTrails | Yes |
+| Censys | Yes |
+| Chaos (ProjectDiscovery) | Yes |
+| AlienVault OTX | No |
+| HackerTarget | No |
+
+## Python Libraries
+
+| Library | Version | Purpose |
+|---------|---------|---------|
+| `subprocess` | stdlib | Execute subfinder, httpx, dnsx CLI |
+| `json` | stdlib | Parse JSON lines output |
+| `pathlib` | stdlib | File path management |
+
+## References
+
+- Subfinder GitHub: https://github.com/projectdiscovery/subfinder
+- httpx GitHub: https://github.com/projectdiscovery/httpx
+- dnsx GitHub: https://github.com/projectdiscovery/dnsx
+- Subfinder Config: https://docs.projectdiscovery.io/tools/subfinder/install