docs: clarify auth in Codex CLI instructions

[RossTarrant]

Summary

Updates the Codex installation guide so the CLI setup command configures the required bearer token environment variable for the hosted GitHub MCP server.

Why

Fixes #2421

The existing Codex CLI example only stored the remote MCP server URL, which produced an unauthenticated config and could leave users in a confusing 401 state.

What changed

• Updated docs/installation-guides/install-codex.md to add --bearer-token-env-var GITHUB_PAT_TOKEN to the codex mcp add example.
• Added a short note explaining that the bearer token environment variable is required for PAT-authenticated access to the hosted GitHub MCP server.

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

• N/A

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

The docs now direct users to configure Codex to read the PAT from GITHUB_PAT_TOKEN instead of creating an unauthenticated remote server entry.

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
• I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/testipt/test`

Docs-only change. Validated the documented codex mcp add github --url https://api.githubcopilot.com/mcp/ --bearer-token-env-var GITHUB_PAT_TOKEN command writes bearer_token_env_var = "GITHUB_PAT_TOKEN" to ~/.codex/config.toml.

Docs

• Not needed
• Updated (README / docs / examples)

[Copilot]

Pull request overview

Updates the Codex installation guide to ensure the Codex CLI example produces an authenticated remote MCP server configuration for the hosted GitHub MCP server, avoiding confusing 401 failures.

Changes:

• Updated the codex mcp add example to include --bearer-token-env-var GITHUB_PAT_TOKEN.
• Added a brief note explaining that the bearer token env var is required for PAT-authenticated access.

Show a summary per file

File	Description
docs/installation-guides/install-codex.md	Fixes the Codex CLI example to include bearer token env var configuration and clarifies the auth requirement.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1