refactor: separa config embedding in ingestion/config.py

- ingestion/config.py (nuovo): EMBED_MODEL, EMBED_MAX_CHARS, OLLAMA_URL
- config.py radice: rimossi EMBED_MODEL e EMBED_MAX_CHARS — resta solo la config RAG
- ingest.py: importa da ingestion.config
- rag.py, retrieve.py: importano EMBED_MODEL da ingestion.config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rag.py

@@ -30,12 +30,12 @@ import chromadb
 
 sys.path.insert(0, str(Path(__file__).parent))
 import config as _cfg
+from ingestion.config import EMBED_MODEL
 
 project_root = Path(__file__).parent
 CHROMA_DIR   = project_root / "chroma_db"
 
 OLLAMA_URL    = _cfg.OLLAMA_URL
-EMBED_MODEL   = _cfg.EMBED_MODEL
 LLM_MODEL     = _cfg.OLLAMA_MODEL
 TOP_K         = _cfg.TOP_K
 TEMPERATURE   = _cfg.TEMPERATURE