chore(deps): anthropic 1.5, openai 3.13, and the move to httpx2

Both SDKs' 1.x/3.x majors run on httpx2 (the maintained fork of httpx by its
original author, published by Pydantic at github.com/pydantic/httpx2, version
line 2.x) instead of httpx, which is what makes these two bumps one change.
httpx2 is now a declared dependency because two modules import it directly.
Everything else in the 0.x -> 1.x / 2.x -> 3.x change lists is absent here:
no Text Completions, no `with_raw_response`, no raw `output_format` dicts, no
Bedrock client, and `requires-python` is already 3.12.

Three code changes, all forced by the bump:

The BYOM DNS-pinning client in `docsgpt/security/safe_url.py` is handed to
`OpenAI(http_client=...)`, and the SDK rejects an old-httpx client at
construction — which would have taken the SSRF guard offline. It is built on
httpx2 now, and its `sni_hostname` extension carries a `str` rather than
ascii bytes: httpcore passes the value straight to
`ssl.SSLContext.wrap_socket`, and the truststore backend httpx2 uses for the
default system trust store encodes it instead of accepting bytes. Bytes
therefore failed every real handshake while passing the existing tests, which
stub the transport out; the test now pins the type and says why.

The stream-retry error tuple in `docsgpt/llm/base.py` named `httpx`
exceptions only. The two libraries' exception classes are unrelated types, so
after the bump the retry silently stopped firing for openai and anthropic
while still working for google-genai and elevenlabs. It now covers both
stacks, with a parametrized test over each.

anthropic 1.x dropped temperature/top_p/top_k from `messages.create`'s
signature (passing one raises TypeError) without dropping them from the API,
so the provider forwards them through `extra_body`. The wire request is
unchanged and a model that rejects them 400s exactly as before.

tests/core/test_byom_user_aware_helpers.py

@@ -416,12 +416,15 @@ class TestSecurityDispatchSSRFGuard:
     def test_dispatch_injects_pinned_http_client_for_user_model(
         self, pg_conn
     ):
-        """LLMCreator must build a DNS-rebinding-safe httpx.Client and
+        """LLMCreator must build a DNS-rebinding-safe httpx2.Client and
         forward it to the OpenAI SDK so the SDK's request-time DNS
         lookup cannot escape the create-time SSRF guard. ``validate_
         user_base_url`` alone is TOCTOU and does not close the
-        rebinding window — the pinned client is what does."""
-        import httpx
+        rebinding window — the pinned client is what does. The client
+        must be httpx2's: the OpenAI SDK rejects an old-httpx client
+        at construction, which would take the guard offline.
+        """
+        import httpx2
 
         from docsgpt.core.model_settings import (
             AvailableModel,
@@ -474,7 +477,7 @@ class TestSecurityDispatchSSRFGuard:
 
         client = captured["http_client"]
         try:
-            assert isinstance(client, httpx.Client), (
+            assert isinstance(client, httpx2.Client), (
                 "http_client must be set for user-source models so the "
                 "OpenAI SDK doesn't re-resolve DNS at request time"
             )