Move old frontend, parser, scraper, and retriever services to legacy/
folder as part of architectural refactor. New agent-based retriever and
pusher services replace the legacy implementation.

- Migrate legacy services to legacy/services/
- Move legacy docker-compose and Makefile to legacy/
- Preserve database schemas in legacy/database/
- New services use agent-based architecture

Preserve old implementation for reference:
- services/frontend/ → legacy/services/frontend/
- services/parser/ → legacy/services/parser/
- services/scraper/ → legacy/services/scraper/
- services/retriever/ (old) → legacy/services/retriever/
- docker-compose.yml → legacy/docker-compose.yml
- docker-compose.override.yml → legacy/docker-compose.override.yml
- Makefile → legacy/Makefile
- database/ → legacy/database/

Add Neo4j client module to retriever service:
- services/retriever/agent/clients/neo4j_client.py
- Update config.py with Neo4j settings

Implement core agent architecture:
- Orchestrator: routes queries and manages conversation flow
- DBQueryAgent: generates and executes Neo4j Cypher queries
- SafetyGuard: validates queries and enforces safety constraints

Complete retriever service implementation:
- FastAPI endpoints for chat and query
- Service configuration and Dockerfile
- Dependencies (pyproject.toml, uv.lock)

New service for multimodal event submission:
- Basic API structure with health endpoint
- Configuration and Dockerfile
- Observability integration

Update infrastructure to support new services:
- docker-compose.yml: retriever and pusher services
- docker-compose.override.yml: development configuration
- Makefile: new service commands
- Dev-container: update dev-container