WIP: add root ai command for AI-assisted project generation

[stevenle]

Motivation

• Provide a first-party CLI entrypoint to run an AI "thinking" model that can generate or edit project code and (when available) CMS docs for Root.js projects.

Description

• Add a new CLI command root ai [prompt...] wired into @blinkk/root's CLI and exported from the CLI module (packages/root/src/cli/cli.ts).
• Implement the one-shot AI workflow in packages/root/src/cli/ai.ts, which accepts prompt input from args or stdin and supports --api-key, --model, --yes, --dry-run, and --json flags.
• Inspect the project context (routes, templates, schemas, docs) and detect if @blinkk/root-cms is present to enable CMS-aware prompting so the model may edit docs when appropriate.
• Call Gemini's generateContent endpoint with a Root.js-specific system prompt, parse and validate a structured JSON response that lists file changes, and safely write generated files only inside the project root.

Testing

• Attempted to run pnpm --filter @blinkk/root build to validate the package build, but the command failed in this environment because Corepack could not download pnpm due to a network/proxy error (Proxy response (403) !== 200 when HTTP Tunneling).
• No automated tests were executed successfully in this environment due to the network restriction preventing package manager operations.

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Codex Task