Add .env.example, demo.tape, and replace hardcoded API key with environment variable

- Add .env.example with templates for all API keys
- Create demo.tape for VHS to generate demo.gif
- Replace hardcoded 'sk-or-...' with $OPENROUTER_API_KEY in README.md
- Add note about setting OPENROUTER_API_KEY before running

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: claude

.env.example

@@ -0,0 +1,20 @@
+# OpenAI API Key (default provider)
+OPENAI_API_KEY=sk-...
+
+# Anthropic API Key
+ANTHROPIC_API_KEY=sk-ant-...
+
+# OpenRouter API Key
+OPENROUTER_API_KEY=sk-or-v1-...
+
+# Generic LLM API Key (alternative to provider-specific keys)
+# LLM_API_KEY=...
+
+# LLM Provider (openai or anthropic)
+# LLM_PROVIDER=openai
+
+# LLM Model (optional, uses provider default if not set)
+# LLM_MODEL=gpt-4o
+
+# Base URL for OpenAI-compatible providers (OpenRouter, Ollama, etc.)
+# LLM_BASE_URL=https://openrouter.ai/api/v1

README.md

@@ -381,10 +381,12 @@ export LLM_MODEL='claude-sonnet-4-20250514'
 
 ```bash
 export LLM_BASE_URL='https://openrouter.ai/api/v1'
-export OPENAI_API_KEY='sk-or-...'
+export OPENAI_API_KEY="$OPENROUTER_API_KEY"
 export LLM_MODEL='anthropic/claude-3.5-sonnet'
 ```
 
+> Note: Set `OPENROUTER_API_KEY` environment variable with your OpenRouter API key before running.
+
 **Local (Ollama)**
 
 ```bash