chore: replace a real LAN address with documentation examples

Pre-publication audit of the full history (all 14 commits, every blob)
found no API keys, tokens, JWTs, private keys or credentials -- the
`user:secret@` strings in the tests are synthetic literals. It did find
one piece of personal infrastructure: 192.0.2.10:4000, a real
RFC1918 host, in 8 places.

Most of those are test fixtures, but one was shipping to users:
strings.json's base_url data_description used it as *the* example in the
config flow, so every install would have displayed a stranger's
internal LiteLLM address as the suggested endpoint. That is a bug
independent of whether this repo is public.

- strings.json: example is now http://litellm.local:4000/v1
- tests: 192.0.2.10 (RFC 5737 TEST-NET-1, reserved for documentation,
  so it can never collide with a real host)

Not addressed here: the address remains in the 14 commits of git
history, which publishing would expose. Scrubbing that needs a history
rewrite, which is a separate decision. The commit author email is
likewise in every commit and would become public.

Local: 137 passed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NxJYWgGJtCw13qUHZtG8ki

custom_components/openai_compatible/strings.json

@@ -30,7 +30,7 @@
         },
         "data_description": {
           "api_key": "Your OpenAI API key.",
-          "base_url": "The OpenAI-compatible endpoint, e.g. http://192.0.2.10:4000/v1 for LiteLLM. Must support the Responses API."
+          "base_url": "The OpenAI-compatible endpoint, e.g. http://litellm.local:4000/v1 for LiteLLM. Must support the Responses API."
         },
         "description": "Set up OpenAI Conversation integration by providing your OpenAI API key. Instructions to obtain an API key can be found [here]({instructions_url})."
       }