Add a0_lemonade plugin

[neurocis]

Adds the a0_lemonade plugin to the Plugin Index.

• Repository: https://github.com/neurocis/A0_Lemonade
• Provider: Lemonade — OpenAI-compatible LLM provider for both chat and embedding models
• LiteLLM: uses litellm_provider: openai with custom_llm_provider: openai so arbitrary local Lemonade model names work
• No hardcoded api_base — user configures the endpoint per-model via Model Configuration
• License: MIT

[a0-bot]

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