fix: strip whitespace from host values

[lin-hongkuan]

Summary

• Strip leading and trailing whitespace before parsing explicit host values.
• Cover host strings with schemes, ports, and paths.

Why

Values copied into OLLAMA_HOST or passed as a host argument can include surrounding whitespace. Without trimming, host parsing can produce an invalid base URL or raise while parsing the port.

Testing

• python -m pytest tests/test_client.py::test_parse_host_strips_whitespace tests/test_client.py::test_headers -q
• git diff --check

[vaderollama]

LGTM — strips whitespace from host values before parsing, preventing invalid base URLs from copy-pasted OLLAMA_HOST values with trailing spaces/newlines. Tests cover scheme, port, and path combinations with spaces, tabs, and newlines. Small and correct.

@ParthSareen — ready to merge.