v0.155.0

BREAKING CHANGE

• the nc_semantic_search_answer MCP tool is removed.
  Clients wanting a generated answer should call nc_semantic_search and
  generate from the returned documents themselves. The
  OLLAMA_GENERATION_MODEL, OPENAI_GENERATION_MODEL and
  BEDROCK_GENERATION_MODEL settings are removed and now ignored.

Feat

• mcp: remove MCP sampling, text generation and the RAG eval harness

Fix

• retry: cap the first retry delay at max_delay

Refactor

• retry: reuse the shared backoff helper for the startup probes
• config: derive the field→env map from Settings
• providers: collapse the duplicate embedding package into providers/
• viz: drop dead settings store and stray template blanks
• viz: drop dead Plotly CDN load and stale viz-UI docs
• viz: remove the in-repo vector-visualization UI