Add LLM preset selection to project create/edit flows, backed by _model_config scoped project config. Support global, project, and combined preset APIs with explicit metadata while preserving plain YAML preset files. Copy selected preset chat/utility settings into project-scoped config, keep embedding settings from the effective config, and document/test the new project model config paths.
- Uses 'git -c http.extraHeader=Authorization: Basic <base64>' for authentication
- Token is encoded as 'base64("x-access-token:TOKEN")' following GitHub's Basic Auth format
- Token is never stored in URL, git config, or project metadata
- 'GIT_TERMINAL_PROMPT=0' prevents interactive credential prompts
- Remote URL displayed in UI always has auth info stripped for security