Bind OP25 control API and terminal to loopback by default

Both :8001 (FastAPI control API) and :8081 (OP25's HTTP terminal) listened on
0.0.0.0 with no authentication, on a container that is privileged with /dev
mounted and network_mode: host. Nodes get deployed to third-party sites, so
that exposed start/stop/retune to anyone on the host's LAN.

All three containers share the host network namespace, so edge-node still
reaches both over 127.0.0.1 unchanged. OP25_DEBUG_EXPOSE=true restores the
old 0.0.0.0 binding and logs a loud warning; it is off by default.

Confirmed against boatbod/op25 gr310 that the terminal's http:<host>:<port>
string is honoured as a real bind address (http_server.py splits it and hands
the host to create_server), so no flag was invented.

Also reorder models.py so IcecastConfig precedes ConfigGenerator, which
annotates a field with it. That only worked because python:slim-trixie is
currently Python 3.14, where PEP 649 defers annotation evaluation; on 3.13 or
earlier the same file is a hard NameError at import.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

op25-container/requirements.txt

@@ -1,2 +1,3 @@
 uvicorn
-fastapi
+fastapi
+pydantic-settings