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/implementing-log-integrity-with-blockchain/references/api-reference.md

@@ -0,0 +1,56 @@
+# API Reference: Log Integrity with Blockchain Hash Chaining
+
+## hashlib - SHA-256 Hashing
+```python
+import hashlib
+hash_hex = hashlib.sha256("data".encode("utf-8")).hexdigest()
+# Returns 64-char hex string
+```
+
+## Chain Entry Structure
+```json
+{
+  "index": 0,
+  "timestamp": "2024-01-15T10:30:00.000Z",
+  "content_hash": "SHA256(log_entry_text)",
+  "prev_hash": "0000...0000 (genesis) or previous chain_hash",
+  "chain_hash": "SHA256(prev_hash + timestamp + content_hash)",
+  "content_preview": "first 200 chars of log entry"
+}
+```
+
+## Chain Construction Algorithm
+```
+genesis_hash = "0" * 64
+for each log_entry:
+    content_hash = SHA256(log_entry)
+    chain_hash = SHA256(prev_hash + timestamp + content_hash)
+    store(index, timestamp, content_hash, prev_hash, chain_hash)
+    prev_hash = chain_hash
+```
+
+## Verification Algorithm
+```
+prev_hash = genesis_hash
+for each entry in chain:
+    expected = SHA256(prev_hash + entry.timestamp + entry.content_hash)
+    if expected != entry.chain_hash:
+        TAMPER DETECTED at index
+    prev_hash = entry.chain_hash
+```
+
+## Checkpoint Structure
+```json
+{
+  "timestamp": "2024-01-15T12:00:00Z",
+  "chain_length": 1000,
+  "head_hash": "chain_hash of last entry",
+  "head_index": 999,
+  "checkpoint_hash": "SHA256(chain_length + head_hash)"
+}
+```
+
+## Tamper Detection Properties
+- Modifying any entry invalidates all subsequent chain_hashes
+- First break index identifies the tampered entry
+- Checkpoint comparison detects retroactive modifications