add LLM suggestion adapter and review flow (opt-in)

[thopatevijay]

• Implement a small adapter packages/cli/src/llm.ts calling OpenAI (or mock).

• Add --auto-llm and --llm-review flags.

• Save suggestions to out/.castui/llm-suggestions.json.

• Implement small web-based review page accessible in generated app to accept/reject suggestions (or CLI prompt to apply them).

Acceptance criteria

• LLM adapter can be executed with --auto-llm=false to return suggestions but not apply them.

• --llm-review opens a review JSON or prints suggestions for acceptance.