fix: use the pooled client timeout for the Anthropic Messages passthrough (#27675)

* fix: use the pooled client timeout for the Anthropic Messages passthrough

The native `/api/v1/messages` passthrough still referenced `openai.AIOHTTP_CLIENT_TIMEOUT`, which stopped existing when `routers/openai.py` moved onto `session_pool.get_client_timeout()`. Every passthrough request therefore raised `AttributeError: module 'open_webui.routers.openai' has no attribute 'AIOHTTP_CLIENT_TIMEOUT'` before it was sent, and the surrounding handler turned that into a 502 "Open WebUI: Server Connection Error", so Anthropic-format clients such as Cline could not reach any model at all.

Use `get_client_timeout(stream=...)` like the OpenAI and Ollama proxies do, so the configured `AIOHTTP_CLIENT_TIMEOUT` applies and streaming requests additionally get the idle-read timeout.

Fixes #27595

* fix: authenticate native Anthropic requests with x-api-key

The Anthropic Messages passthrough and the token-count forwarding both build their upstream request through `get_anthropic_request_target`, which sends the connection key as `Authorization: Bearer <key>`. Anthropic's OpenAI-compatible `/chat/completions` endpoint accepts that, which is why the model works in the chat UI, but the native `/v1/messages` and `/v1/messages/count_tokens` endpoints do not: they require the key in `x-api-key` and reject a bearer token with 401 `Invalid bearer token` (and `jwt auth is not yet supported on count_tokens`). They also require an `anthropic-version` header, which was never sent.

For `api.anthropic.com` connections, send `anthropic-version` and move the key into `x-api-key`, dropping the bearer header. Connections using session, OAuth or Entra ID auth keep their token untouched, LiteLLM passthrough connections are unaffected, and admin-configured custom headers still win over both defaults.

Fixes #27695

backend/open_webui/utils/anthropic.py

@@ -12,6 +12,8 @@ from open_webui.utils.json_codec import JSONCodec
 
 log = logging.getLogger(__name__)
 
+ANTHROPIC_VERSION = '2023-06-01'
+
 ANTHROPIC_CONVERTED_REQUEST_PARAMS = {
     'model',
     'messages',
@@ -48,7 +50,7 @@ async def get_anthropic_models(url: str, key: str, user: UserModel = None) -> di
         async with aiohttp.ClientSession(timeout=timeout, trust_env=True) as session:
             headers = {
                 'x-api-key': key,
-                'anthropic-version': '2023-06-01',
+                'anthropic-version': ANTHROPIC_VERSION,
             }
 
             if ENABLE_FORWARD_USER_INFO_HEADERS and user: