Revive terminal dotfiles setup

[ma08]

Summary

• Restore the GCP terminal baseline from ~/pro/dotfiles: Linuxbrew Neovim, ranger, and GitUI; portable editor/ranger/GitUI links; and automatic backup of the former Azure-target Neovim/Vim links.
• Keep CodeCompanion chat on the ChatGPT-authenticated Codex ACP route.
• Replace CodeCompanion inline editing's Azure OpenAI gpt-5.5 adapter with Gemini gemini-3.6-flash, non-streaming and at minimal thinking for responsive inline edits.
• Document the machine-local GEMINI_API_KEY requirement without storing a credential in dotfiles.

Validation

• git diff --check
• ~/pro/dotfiles/setup.sh --editor --ranger --git --apply on research-cpu-01
• Headless Neovim/CodeCompanion adapter resolution; model gemini-3.6-flash, non-streaming, minimal thinking
• Bounded Gemini Developer API smoke test: HTTP 200, one candidate, first response part is text (the shape CodeCompanion's inline handler requires)
• nvim --version, ranger --version, and gitui --version on the GCP host

Notes

• The Gemini credential is service-account-bound and restricted to the Generative Language API in ladduu-ai-agent; its value exists only in ignored local botfiles secrets.
• The four pre-existing tracked ranger .pyo deletions remain intentionally unstaged and are not part of this PR.
• The required botfiles secret-loader allowlist change is kept as a separate, minimal PR.

Written by Codex via the developer's authenticated GitHub account.