Align agentic-retrieval-pipeline-example notebook with validated KB flow

- Surface 'Knowledge Bases' and 'Foundry IQ' terminology in notebook title/description
- Add AzureKeyCredential support: optional AZURE_SEARCH_API_KEY and AZURE_OPENAI_API_KEY
- Add azure_openai_resource_endpoint() helper to normalize endpoint URLs
- Use search_credential throughout all Search SDK calls
- Add semantic_configuration_name and page_chunk field to knowledge source parameters
- Remove KnowledgeRetrievalOutputMode enum; use output_mode='extractiveData' string
- Fix MCP endpoint API version: 2025-11-01-Preview -> 2026-05-01-preview
- Add endpoint.rstrip('/') to MCP URL construction
- Add timeout=60 to requests.get for document download
- Fix extra_body key: 'agent_reference' -> 'agent' in responses.create
- Fix delete_index(index) -> delete_index(index_name) in cleanup cell
- Add optional AZURE_SEARCH_API_KEY and AZURE_OPENAI_API_KEY to sample.env

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mattgotteiner