Ingestion: versioned extraction policy profiles for add_event

[aurexav]

Summary

Introduce versioned ingestion policy profiles for add_event so extraction behavior is configurable, testable, and rollback-safe.

Why

ELF's deterministic boundary is a core strength. We still need controlled flexibility for extraction prompt/rules without ad-hoc edits.

Scope

• Define ingestion_profile object and versioning model.
• Add profile selection to POST /v2/events/ingest (explicit or default profile).
• Profile fields include:
  • extraction prompt template id
  • optional few-shot references
  • schema version
  • confidence gates and fallback strategy
• Persist profile id/version with each write for audit and replay.

Acceptance Criteria

• Same input + same profile version yields reproducible extraction behavior.
• Profile change does not affect historical writes retroactively.
• API can report which profile version produced each note.

Related

• Viewer: add retrieval observability panels on top of #26 #41
• Add a read-only web viewer for sessions and traces #26