Add OpenRouter support and improve JSON parsing robustness

- Add OpenRouter as third LLM provider option in config.py
- Implement _extract_json() to handle markdown-wrapped JSON responses
- Add default values for missing required fields in ScriptPlan
- Handle navigation_strategy as list or string
- Add .env.example with configuration templates
- Add test script and sample generated scrapers for RWTH and KAUST

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.env.example

@@ -0,0 +1,14 @@
+# OpenRouter Configuration (recommended)
+CODEGEN_MODEL_PROVIDER=openrouter
+OPENAI_API_KEY=your-openrouter-api-key-here
+CODEGEN_OPENROUTER_MODEL=anthropic/claude-sonnet-4
+
+# Alternative: Direct Anthropic
+# CODEGEN_MODEL_PROVIDER=anthropic
+# ANTHROPIC_API_KEY=your-anthropic-api-key-here
+# CODEGEN_ANTHROPIC_MODEL=claude-sonnet-4-20250514
+
+# Alternative: OpenAI
+# CODEGEN_MODEL_PROVIDER=openai
+# OPENAI_API_KEY=your-openai-api-key-here
+# CODEGEN_OPENAI_MODEL=gpt-4o