Add per-service customization, stealth hardening, and BYOS support

- HTTP: configurable server_header, response_code, fake_app presets
  (apache/nginx/wordpress/phpmyadmin/iis), extra_headers, custom_body,
  static files directory mount
- SSH/Cowrie: configurable kernel_version, hardware_platform, ssh_banner,
  and users/passwords via COWRIE_USERDB_ENTRIES; switched to build mode
  so cowrie.cfg.j2 persona fields and userdb.txt generation work
- SMTP: configurable banner and MTA hostname
- MySQL: configurable version string in protocol greeting
- Redis: configurable redis_version and os string in INFO response
- BYOS: [custom-*] INI sections define bring-your-own Docker services
- Stealth: rename all *_honeypot.py → server.py; replace HONEYPOT_NAME
  env var with NODE_NAME across all 22+ service templates and plugins;
  strip "honeypot" from all in-container file content
- Config: DeckyConfig.service_config dict; INI [decky-N.svc] subsections;
  composer passes service_cfg to compose_fragment
- 350 tests passing (100%)

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

decnet/custom_service.py

@@ -0,0 +1,41 @@
+"""
+Bring-your-own-service (BYOS) support.
+
+CustomService wraps a user-defined service from an INI [custom-*] section.
+It is instantiated dynamically and registered via register_custom_service(),
+not through the auto-discovery mechanism in the registry.
+"""
+
+from decnet.services.base import BaseService
+
+
+class CustomService(BaseService):
+    """A user-defined service that runs an arbitrary Docker image."""
+
+    def __init__(self, name: str, image: str, exec_cmd: str, ports: list[int] | None = None):
+        self.name = name
+        self.default_image = image
+        self.ports = ports or []
+        self._exec_cmd = exec_cmd
+
+    def compose_fragment(
+        self,
+        decky_name: str,
+        log_target: str | None = None,
+        service_cfg: dict | None = None,
+    ) -> dict:
+        slug = self.name.replace("_", "-")
+        fragment: dict = {
+            "image": self.default_image,
+            "container_name": f"{decky_name}-{slug}",
+            "restart": "unless-stopped",
+            "environment": {"NODE_NAME": decky_name},
+        }
+        if self._exec_cmd:
+            fragment["command"] = self._exec_cmd.split()
+        if log_target:
+            fragment["environment"]["LOG_TARGET"] = log_target
+        return fragment
+
+    def dockerfile_context(self):
+        return None