fix: Update _extract_and_emit_metrics for flattened data structure

Refactor: Source-keyed output format across all MCP servers

Fix end_date emission for valuation, volatility, and macro metrics

Add schema normalizers for MCP output consistency

Fix news metric extraction - use 'results' field

Fix mcp_client.py - restore nested financials/debt access

Fix temporal data for calculated metrics (margins, debt_to_equity)

Refactor emit_metric to use structured payload dict

Add comprehensive null checks in _extract_and_emit_metrics

Add status messages for empty news/sentiment data

Add temporal data streaming to A2A partial_metrics

Initial commit: Researcher Agent