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>

.gitignore

@@ -174,3 +174,8 @@ cython_debug/
 # PyPI configuration file
 .pypirc
 
+# Windows artifacts
+nul
+
+# Scraper output files
+*_results.json