feat(ollama): respect OLLAMA_HOST env var for remote connections

[grgomez]

Description:

Automatically read the OLLAMA_HOST environment variable (the same variable used by the Ollama CLI) to configure
the base URL for the Ollama adapter. This allows users to connect to a remote Ollama instance without any Neovim
configuration — simply setting OLLAMA_HOST in the shell is sufficient. Falls back to http://localhost:11434 when
the variable is not set.

This benefits users running Ollama on a separate machine (e.g. a home server or cloud VM) who expect the standard
Ollama environment variable to be respected, as it is by the Ollama CLI itself.

AI Usage:

This PR was developed with the assistance of Claude Code (claude-haiku-4-5) to identify the correct integration
point and update the documentation.

Related Issues:

None

Screenshots:

Not applicable

Checklist:

• I've read the contributing
  guidelines and have adhered to them in this PR
• I confirm that this PR has been majority created by me, and not AI (unless stated in the "AI Usage"
  section above)
• I've run make all to ensure docs are generated, tests pass and StyLua has formatted the code
• (optional) I've added tests/adapters/http/test_ollama.lua test coverage for this
  fix/feature
• (optional) I've updated the README and/or relevant docs pages

[olimorris]

Perfect PR! Thank you.