feat(installer): support project-local Codex installs (#1531) (#1551)

Codex CLI has a first-class project config layer — `.codex/config.toml`
is layer 4 of the loader stack, above the user config at layer 6
(`codex-rs/config/src/loader/README.md` in openai/codex), and it landed
in openai/codex#8354 on 2025-12-22. The CodexTarget's "Codex has no
project-local config concept" note was therefore never accurate, and
`supportsLocation('local') === false` made Codex the one agent that
forces a machine-wide MCP install.

`mcp_servers` is not on the project layer's denylist (which strips base
URLs, model providers, `notify`, profiles and otel — settings repo
contents shouldn't choose), so a project-scoped `[mcp_servers.codegraph]`
is honored.

- Path helpers take a `Location`: global keeps `~/.codex/config.toml` +
  `~/.codex/AGENTS.md`; local writes `<cwd>/.codex/config.toml` and the
  project-root `<cwd>/AGENTS.md` — the same split the gemini and
  opencode targets already use for their local layout.
- Drops the five `loc !== 'global'` early returns from detect, install,
  uninstall, printConfig and describePaths.
- Local install returns a note that Codex only applies a project layer
  in a project marked trusted; untrusted projects load the layer but
  leave it disabled, so a silent success would be misleading.
- Refreshes the two doc comments that used Codex as the example of a
  global-only target (now the Copilot CLI).

Tests: two new cases covering the local write layout, the trust note,
global config staying untouched, and local uninstall leaving the global
entry intact. Both fail against the previous implementation. The generic
per-target contract suite now also exercises codex at location=local.

CHANGELOG.md

@@ -19,6 +19,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 - GitHub Copilot is now a supported agent: `codegraph install` can configure Copilot Chat in VS Code (`copilot-vscode`), the GitHub Copilot CLI (`copilot-cli`), and the Copilot plugin in JetBrains IDEs (`copilot-jetbrains`). Installed Copilot surfaces are auto-detected like every other agent, existing MCP server entries in their config files are preserved, and `codegraph uninstall` reverses the setup cleanly. Restart VS Code or your JetBrains IDE after installing so Copilot picks up the server.
 
+- Codex CLI can now be set up per project instead of only user-wide: `codegraph install --location=local` writes `./.codex/config.toml` and the CodeGraph block in your project's `AGENTS.md`, so CodeGraph is wired into that repo only rather than every Codex session on the machine. `codegraph uninstall --location=local` reverses it, and the global install is untouched either way. Codex only applies a project's config once you've marked the project trusted, so the installer says so after a local install. (#1531)
+
 ### Fixes
 
 - Import aliases defined in a shared TypeScript config are now picked up. Nx-style monorepos keep every `@scope/...` alias in a `tsconfig.base.json` that the root `tsconfig.json` only inherits through `extends`, so CodeGraph found no aliases at all and every cross-package import fell back to matching on name alone — which quietly attaches results to unrelated symbols that happen to share a name, exactly where a monorepo needs `codegraph_impact` and `codegraph_callers` to be right. Chains several configs deep, a config inherited from a package in `node_modules`, and a `baseUrl` declared in an inherited config are all followed now, and a `tsconfig.base.json` is read directly when the root `tsconfig.json` is only a project-references shell or isn't there at all. Re-index after upgrading. (#1534)