Warn when the peripheral API binds to a non-loopback address

[sappafrancesco]

Fixes #400.

The peripheral WebSocket API defaults to 0.0.0.0 and has no
authentication. That combination isn't flagged anywhere at runtime,
and docs/peripheral_api.md's "No authentication is required." reads
as a convenience note rather than a warning.

Per the issue discussion, keeping 0.0.0.0 as the default isn't
obviously wrong (some setups genuinely want to control LVA from
another device or container), so this doesn't change it. What it does:

• Logs a warning at startup whenever --peripheral-host resolves to
  anything other than 127.0.0.1/::1/localhost, naming the
  concrete things an unauthenticated LAN client could do (mute/unmute
  the mic, start_listening to open a voice pipeline and stream
  captured audio to whatever conversation agent is configured, change
  the volume, register arbitrary entities) and pointing at
  --peripheral-host 127.0.0.1.
• Expands the docs line to spell out what "no authentication" plus the
  0.0.0.0 default actually means, and how to opt out of it.

Type of change

• Bugfix (non-breaking change which fixes an issue)

Testing

Added:

• test_start_warns_on_non_loopback_host
• test_start_does_not_warn_on_loopback_host (parametrized over
  127.0.0.1, ::1, localhost)

black --check / isort --check / flake8 / mypy / pylint -> clean
pytest tests/unit/test_peripheral_api.py -> 88 passed
pytest tests/ -> same 49 pre-existing failures in test_satellite.py as
  on main with this diff stashed out (an audio/OS-level test
  environment issue unrelated to and untouched by this change)