Label R2R Langfuse traces

[finnp]

Summary

• label R2R search query embeddings as r2r-search
• label indexing embeddings, enrichment, document summaries, VLM parsing, and audio transcription as r2r-indexing
• preserve r2r as the fallback trace name while allowing operation-specific overrides

Verification

• ruff check on all changed files
• ruff format --check on all changed files
• Python compile check on all changed files
• ingestion unit tests: 2 passed