Add 20 honeypot services: email, DB, ICS, cloud, IoT, network protocols

Tier 1 (upstream images): telnet (cowrie), smtp (mailoney),
elasticsearch (elasticpot), conpot (Modbus/S7/SNMP ICS).

Tier 2 (custom asyncio honeypots): pop3, imap, mysql, mssql, redis,
mongodb, postgres, ldap, vnc, docker_api, k8s, sip, mqtt, llmnr, snmp,
tftp — each with Dockerfile, entrypoint, and protocol-accurate
handshake/credential capture.

Adds 256 pytest cases covering registration, compose fragments,
LOG_TARGET propagation, and Dockerfile presence for all 25 services.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

decnet/services/telnet.py

@@ -0,0 +1,31 @@
+from decnet.services.base import BaseService
+
+
+class TelnetService(BaseService):
+    name = "telnet"
+    ports = [23]
+    default_image = "cowrie/cowrie"
+
+    def compose_fragment(self, decky_name: str, log_target: str | None = None) -> dict:
+        env: dict = {
+            "COWRIE_HONEYPOT_HOSTNAME": decky_name,
+            "COWRIE_TELNET_ENABLED": "true",
+            "COWRIE_TELNET_LISTEN_ENDPOINTS": "tcp:23:interface=0.0.0.0",
+            # Disable SSH so this container is telnet-only
+            "COWRIE_SSH_ENABLED": "false",
+        }
+        if log_target:
+            host, port = log_target.rsplit(":", 1)
+            env["COWRIE_OUTPUT_TCP_ENABLED"] = "true"
+            env["COWRIE_OUTPUT_TCP_HOST"] = host
+            env["COWRIE_OUTPUT_TCP_PORT"] = port
+        return {
+            "image": "cowrie/cowrie",
+            "container_name": f"{decky_name}-telnet",
+            "restart": "unless-stopped",
+            "cap_add": ["NET_BIND_SERVICE"],
+            "environment": env,
+        }
+
+    def dockerfile_context(self):
+        return None