chore: upgrade litellm to 1.81.1 for zai provider support

Updates LiteLLM from ~1.80.7 to ~1.81.1 which includes
full support for z.ai (Zhipu AI) provider using the 'zai/model-name'
format. This enables Strix to work with z.ai subscription
credentials by setting STRIX_LLM="zai/glm-4.7" with appropriate
LLM_API_KEY and LLM_API_BASE environment variables.

Changes:
- Updated litellm version constraint in pyproject.toml
- No breaking changes to Strix API or configuration

Closes #ISSUE_ID (to be linked if applicable)

Signed-off-by: legendevent <legendevent@users.noreply.github.com>

pyproject.toml

@@ -47,7 +47,7 @@ strix = "strix.interface.main:main"
 [tool.poetry.dependencies]
 python = "^3.12"
 # Core CLI dependencies
-litellm = { version = "~1.80.7", extras = ["proxy"] }
+litellm = { version = "~1.81.1", extras = ["proxy"] }
 tenacity = "^9.0.0"
 pydantic = {extras = ["email"], version = "^2.11.3"}
 rich = "*"