feat(aichat): add CLI for AI Dialogue service

[Copilot]

Syncs the aichat service into the monorepo by adding a new aichat/ CLI package that wraps the POST /aichat/conversations endpoint per the updated Docs OpenAPI spec.

New package: aichat-cli

• chat command — maps all API parameters: question (arg), -m/--model, --id (continue a conversation), --preset, --stateful, -r/--reference (repeatable)
• models command — lists all 80 supported models (GPT-5.x, GPT-4.x, o1/o3/o4-series, DeepSeek-R1/V3, Grok-3, GLM series)
• config command — shows current token/URL/timeout settings
• Rich terminal output by default; --json for scripting

aichat chat "Explain quantum entanglement" -m deepseek-r1
aichat chat "Continue" --stateful --id 64a67fff-61dc-4801-8339-2c69334c61d6
aichat chat "Summarize" -r https://example.com/paper --json

Follows the established monorepo structure (core/{client,config,exceptions,output}, commands/, Docker, 33 unit tests with respx mocking).