Add CLI agent instrumentation

[zahlekhan]

What changed

• add a global --agent-name option with agent-facing guidance in root and subcommand help
• record the declared value as agent_name, defaulting to unknown
• detect known Codex, Claude Code, Cline, Factory Droid, and Pi markers as detected_agent_name
• return unknown when no marker exists and ambiguous when markers conflict
• record the package manager selected for scaffold dependency installation as package_manager
• document that declared and detected attribution are both spoofable and are not authentication signals

Why

CLI usage needs two independent agent-attribution signals: an explicit declaration that works for any invoking agent and best-effort environment detection when the declaration is omitted. Keeping both fields preserves their provenance and avoids treating either spoofable signal as trusted identity.

Impact

AI agents can pass a stable lowercase kebab-case product slug, for example --agent-name codex. Human invocations can omit the option and retain the unknown default. Create-flow events report the selected npm, pnpm, yarn, or bun installer. Existing telemetry opt-out behavior remains unchanged.

Validation

• TypeScript CLI build
• ESLint on packages/openui-cli/src
• Prettier checks on changed CLI and documentation files