feat: knowledge base with URL import, ADB case-sensitivity fix, and RAG enhancements

- Add Knowledge Base (Base de Conhecimento) with file upload + URL import
- URL content extraction: HTML stripping, remote PDF parsing
- Auto-resolve embedding config from OCI credentials
- Case-insensitive ADB table matching with quoted identifiers
- Table validation endpoint, report_date metadata, purge & re-embed flow
- Embeddings tab cleanup, PyPDF2 dependency, README updated to v2.3

backend/requirements.txt

@@ -7,3 +7,4 @@ oci==2.133.0
 oracledb==2.4.1
 mcp>=1.0.0
 requests>=2.31.0
+PyPDF2>=3.0.0