feat(b2b-marketing): Finalize grounding architecture and frontend improvements

- Upgrade backend to use gemini-2.5-flash with sanitized HTML parsing (no token limit).
- Implement robust retry logic and increased timeouts (600s) for deep analysis.
- Add file-based logging for prompts and responses.
- Fix API endpoint (v1) and regex parsing issues.
- Frontend: Optimize PDF export (landscape, no scrollbars), fix copy-paste button, add 'Repeat Step 6' feature.
- Update documentation to 'Completed' status.

b2b-marketing-assistant/requirements.txt

@@ -0,0 +1,5 @@
+google-generativeai
+requests
+beautifulsoup4
+lxml
+python-dotenv