fix: restore upstream LiteLLM dependency

[nightcityblade]

Summary

Fixes #2098.

Replace the unclecode-litellm fork with the upstream litellm distribution. The lower bound starts after the removed compromised releases, and the temporary <1.92.0 bound keeps installs on the last universal wheel release; LiteLLM 1.92+ does not currently publish macOS wheels and otherwise requires a local Rust build.

List of files changed and why

• pyproject.toml - Declare the safe upstream LiteLLM range in package metadata.
• requirements.txt - Keep development/install requirements synchronized with package metadata.

How Has This Been Tested?

• uvx --with 'packaging>=24.2' --from validate-pyproject validate-pyproject pyproject.toml
• uv pip compile pyproject.toml --no-deps --quiet (resolves litellm==1.91.4)
• uv run --python 3.12 --with toml python tests/check_dependencies.py
• Imported both crawl4ai and upstream litellm from the resolved project environment.
• Built the wheel and verified its Requires-Dist metadata contains only litellm<1.92.0,>=1.83.0.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My code is commented, particularly in hard-to-understand areas — N/A: no executable code changed
• I have made corresponding changes to the documentation — N/A: the dependency declarations are the affected configuration
• I have added/updated unit tests that prove my fix is effective or that my feature works — N/A: this is package metadata; wheel metadata and a resolved import were tested directly
• New and existing relevant tests pass locally with my changes

[nightcityblade]

CI note: the only failing check is the Discord notification job. Its log shows Secret source: None, an empty DISCORD_WEBHOOK, and then Env var DISCORD_WEBHOOK is not defined; it does not install or test this PR’s dependency changes. This is a fork-secret/workflow configuration failure rather than a code failure in the patch.