fix: actually check the endpoint during setup

async_setup_entry handed client.with_options(timeout=10.0).models.list to the
executor. On AsyncOpenAI that returns an awaitable paginator, so it came back
unawaited, no request was made, and a bad key or an unreachable endpoint still
set up. It now awaits client.models.list(timeout=10.0), matching core's
openai_conversation, so a 401 raises ConfigEntryAuthFailed and a connection
error ConfigEntryNotReady, as the README already says.

The shared mock_init_component fixture now patches models.list with an
AsyncMock and keeps the patch for the whole test, because tests that change a
subentry reload the entry and run setup again.

Reported by @MartinNuc in #1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SUd68TsT5QZ68Dtfw2uWBU

custom_components/openai_compatible/__init__.py

@@ -294,7 +294,7 @@ async def async_setup_entry(hass: HomeAssistant, entry: OpenAIConfigEntry) -> bo
     _ = await hass.async_add_executor_job(client.platform_headers)
 
     try:
-        await hass.async_add_executor_job(client.with_options(timeout=10.0).models.list)
+        await client.models.list(timeout=10.0)
     except openai.AuthenticationError as err:
         raise ConfigEntryAuthFailed(err) from err
     except openai.OpenAIError as err: