refactor: Extract shared utilities into ai_brain package

[Ovbosire]

Summary

Extract duplicated code across app.py, query_brain.py, graph_query.py, and ingestion scripts into a shared ai_brain/ package structure, eliminating ~100 lines of duplicated code.

Changes

• ai_brain/query/time_filter.py — Shared time-filter parsing (was duplicated in app.py and query_brain.py)
• ai_brain/graph/driver.py — Shared Neo4j driver with lazy initialization and liveness check (was duplicated across 4 files). Raises ConnectionError instead of calling sys.exit(1).
• ai_brain/query/flat_rag.py — Shared flat RAG vector+keyword search (was duplicated in app.py and query_brain.py)
• ai_brain/query/text_utils.py — Shared STOPWORDS set (was duplicated with slight variations in query_brain.py and graph_query.py)
• app.py — Imports from shared modules; removes ~50 lines of duplicated logic
• query_brain.py — Imports from shared modules; removes ~45 lines of duplicated logic
• graph_query.py — Imports STOPWORDS and Neo4j driver from shared modules; removes ~25 lines
• extract_entities.py — Imports Neo4j driver from shared module; removes ~10 lines
• extract_daemon.py — Imports Neo4j driver from shared module
• neo4j_setup.py — Imports Neo4j driver from shared module; removes ~15 lines

Validation

• Python syntax check passes on all 14 files
• Package structure: ai_brain/, ai_brain/graph/, ai_brain/query/, ai_brain/ingestion/
• All public function signatures preserved exactly
• Each consumer file imports from the single shared source of truth

File Structure

ai_brain/
├── __init__.py
├── graph/
│   ├── __init__.py
│   └── driver.py          # get_neo4j_driver()
├── ingestion/
│   └── __init__.py
└── query/
    ├── __init__.py
    ├── flat_rag.py         # flat_rag_search()
    ├── text_utils.py       # STOPWORDS
    └── time_filter.py      # parse_time_filter()