fix(deps): exclude litellm 1.82.6 (internal ImportError) — #15916 (#15920)

## Summary

Fixes #15916.

A fresh `docker compose -f docker-compose-macos.yml up -d` against
v0.25.6 errors out on container start with

pyproject.toml

@@ -155,7 +155,11 @@ dependencies = [
     #    "xxhash>=3.5.0,<4.0.0",
     #    "trio>=0.17.0,<0.29.0",
     #    "click>=8.1.8",
-    "litellm~=1.82.0,!=1.82.7,!=1.82.8",
+    # 1.82.6 has an internal ImportError loading add_system_prompt_to_messages
+    # from litellm_core_utils.prompt_templates.common_utils, which breaks
+    # `import litellm` at module load and tanks the whole server (#15916).
+    # 1.82.7 / 1.82.8 were already excluded for security in #13768.
+    "litellm~=1.82.0,!=1.82.6,!=1.82.7,!=1.82.8",
     #    "pip>=25.2",
     #    "imageio-ffmpeg>=0.6.0",
     #    "cryptography==46.0.3",