Implement interactive CLI for LLM providers with chat, tools, and image support

- Add Bubble Tea-based CLI interface for LLM interactions.
- Implement `.env.example` for environment variable setup.
- Add provider, model, and tool selection screens.
- Include support for API key configuration.
- Enable chat interactions with optional image and tool support.
- Introduce core utility functions: image handling, tool execution, chat request management, and response rendering.
- Implement style customization with Lip Gloss.

cmd/llm/.env.example

@@ -0,0 +1,11 @@
+# go-llm CLI Environment Variables
+# Copy this file to .env and fill in your API keys
+
+# OpenAI API Key (https://platform.openai.com/api-keys)
+OPENAI_API_KEY=
+
+# Anthropic API Key (https://console.anthropic.com/settings/keys)
+ANTHROPIC_API_KEY=
+
+# Google AI API Key (https://aistudio.google.com/apikey)
+GOOGLE_API_KEY=