feat(openai): add OpenAI CLI tool synced with openapi/openai.json

[Copilot]

The Docs repo openapi/openai.json defines 5 endpoints for an openai service, but no corresponding openai/ CLI subdirectory existed in this monorepo.

New openai/ CLI package

Structure follows existing CLI conventions (serp, nanobanana, etc.):

• commands/chat.py — chat (single message) and complete (JSON messages array) → POST /openai/chat/completions
• commands/embed.py — embed → POST /openai/embeddings
• commands/image.py — imagine and edit-image → POST /openai/images/generations / POST /openai/images/edits
• commands/respond.py — respond → POST /openai/responses
• commands/info.py — models, config
• core/ — client, config, exceptions, output matching the standard pattern

Model coverage (from spec)

Group	Models
Chat/Completions	gpt-5.5, gpt-5.5-pro, gpt-5.4, gpt-5.4-pro, gpt-5.2, gpt-5.1*, gpt-5, gpt-5-mini, gpt-5-nano, gpt-4*, gpt-4o*, o1*, o3*, o4-mini*
Responses API	Extended superset of chat models
Embeddings	text-embedding-3-small, text-embedding-3-large, text-embedding-ada-002
Images	dall-e-3, gpt-image-1, gpt-image-1.5, gpt-image-2, nano-banana*

openai chat "What is the capital of France?" -m gpt-4o-mini
openai embed "The quick brown fox" -m text-embedding-3-large
openai imagine "A serene mountain landscape" --quality high
openai respond "Explain quantum computing" -m o3
openai edit-image "Remove background" -i https://example.com/photo.jpg