docs: document missing config options and fix manager_path bug

[staging-devin-ai-integration]

Summary

Two changes:

1. README: Added documentation for 7 config options defined in lua/codeium/config.lua that were missing from the README: manager_path, language_server_download_url, quiet, enable_local_search, enable_index_service, search_max_workspace_file_count, and file_watch_max_dir_count.

2. Bug fix (lua/codeium/api.lua): config.manager_path → config.options.manager_path. The old code accessed a non-existent field on the config module, so user-provided manager_path was silently ignored and the server always used a temp directory.

Review & Testing Checklist for Human

• Verify the manager_path bug fix doesn't break existing behavior: Before this fix, manager_path always resolved to nil (temp dir fallback). After this fix, if a user had manager_path set in their config, it would actually be used. Confirm no downstream code assumes the manager dir is always a temp directory.
• Spot-check documentation accuracy: Verify that the defaults and descriptions for the 7 newly documented options match lua/codeium/config.lua defaults and the consuming code in api.lua / update.lua.
• Manual test: Set manager_path to a custom directory in your Neovim config, restart, and confirm the language server uses that directory instead of a temp one.

Notes

• All previously documented options were verified as consumed in the codebase — no stale docs.
• No lint tooling or test suite exists in this repo, so validation is manual only.

Link to Devin session: https://localhost:3000/sessions/7c4051b3ecdf4ac3a8b3516012aae980
Requested by: @IdoPesok

[staging-devin-ai-integration]

Original prompt from Ido

Recent commits added several new options to lua/codeium/config.lua: quiet (suppress completion errors), enable_cmp_source, and the full virtual_text subtable with keys like enabled, filetypes, manual, idle_delay, key_bindings, etc. Cross-check each of these options against the README.md to confirm every option is documented with its type, default, and purpose — add any that are missing, and verify each option is actually read and respected in the consuming code.

[staging-devin-ai-integration]

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