refactor: Clean up test files and simplify documentation

- Remove unused cassette files with incomplete recordings
- Delete broken respx test files (test_o3_pro_respx_simple.py, test_o3_pro_http_recording.py)
- Fix respx references in docstrings to mention HTTP transport recorder
- Simplify vcr-testing.md documentation (60% reduction, more task-oriented)
- Add simplified PR template with better test instructions
- Fix cassette path consistency in examples
- Add security note about reviewing cassettes before committing

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

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

tests/test_o3_pro_output_text_fix.py

@@ -1,10 +1,10 @@
 """
-Tests for o3-pro output_text parsing fix using respx response recording.
+Tests for o3-pro output_text parsing fix using HTTP transport recording.
 
 This test validates the fix that uses `response.output_text` convenience field
 instead of manually parsing `response.output.content[].text`.
 
-Uses respx to record real o3-pro API responses at the HTTP level while allowing
+Uses HTTP transport recorder to record real o3-pro API responses at the HTTP level while allowing
 the OpenAI SDK to create real response objects that we can test.
 
 RECORDING: To record new responses, delete the cassette file and run with real API keys.