feat(services): config schemas for the rest of the registry + textarea base64 transport

- Declarative config_schema on RDP, Telnet, MySQL, Redis, SMTP, SMTP_Relay
  matching the keys each service already reads at compose time.
- TODO marker on the 19 services that accept service_cfg but never read it,
  so future contributors know where to plug schemas in.
- Wizard base64-wraps all textarea values at INI emit (DeckyFleet
  buildIni); validate_cfg detects the b64: sentinel and decodes back to
  UTF-8. Plain raw strings still pass through for direct API submitters.
- HTTPS image entrypoint accepts PEM content or path in TLS_CERT/TLS_KEY:
  detects a BEGIN header, writes content to /opt/tls/, and re-exports
  the on-disk path so server.py keeps reading paths.
- Tests cover schema/compose alignment for each new service plus
  textarea base64 round-trip (incl. UTF-8) and HTTPS PEM end-to-end.

decnet/services/telnet.py

@@ -1,7 +1,7 @@
 import os
 from pathlib import Path
 
-from decnet.services.base import BaseService
+from decnet.services.base import BaseService, ServiceConfigField
 
 TEMPLATES_DIR = Path(__file__).parent.parent / "templates" / "telnet"
 ARTIFACTS_ROOT = os.environ.get("DECNET_ARTIFACTS_ROOT", "/var/lib/decnet/artifacts")
@@ -24,6 +24,27 @@ class TelnetService(BaseService):
     ports = [23]
     default_image = "build"
 
+    config_schema = [
+        ServiceConfigField(
+            key="password",
+            label="Root password",
+            type="password",
+            default="admin",
+            secret=True,
+            help="Plaintext root password for the in-container telnetd.",
+        ),
+        ServiceConfigField(
+            key="hostname",
+            label="Container hostname",
+            type="string",
+            placeholder="e.g. mail-01.corp.local",
+            help=(
+                "Cosmetic override for the telnet banner — keeps decoys "
+                "looking heterogeneous. Decky identity (NODE_NAME) is unaffected."
+            ),
+        ),
+    ]
+
     def compose_fragment(
         self,
         decky_name: str,