Add structured logging to ingestion engine

[EduardPetraeus]

Problem

ingestion_engine.py uses print() calls in some places. Should use structured JSON logging with run_id for traceability.

Proposed Solution

• Replace all print() with structured logging (existing logging_config.py pattern)
• Add run_id to all log entries
• JSON structured output parseable by standard tools

Acceptance Criteria

• No print() calls remain in ingestion_engine.py
• JSON structured logging configured
• run_id included in all log entries
• Log output is parseable by standard JSON tools

Migrated from backlog/TASK-002.yaml