feat(chunking): add embedding model registry and ollama config

Why:
- Operators need Cloud and Local Embedding Models with stable ids, dimensions, and defaults.

Changes:
- Add Embedding Model Registry; Ollama client; env defaults for model, Ollama host, and Neighbor Expansion knobs.

Impact:
- New installs default to text-embedding-3-large; OLLAMA_BASE_URL required for Local provider.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/core/config.py

@@ -10,15 +10,21 @@ class Settings(BaseSettings):
 
     # OpenAI
     openai_api_key: str
-    embedding_model: str = "text-embedding-3-small"
+    embedding_model: str = "text-embedding-3-large"
     llm_model: str = "gpt-4o-mini"
 
+    # Local embeddings (Ollama) — Admin switches models; host stays in config
+    ollama_base_url: str = "http://192.168.10.10:11435"
+
     # Qdrant
     qdrant_url: str = "http://localhost:6333"
     qdrant_api_key: str | None = None
 
     # Retrieval
     top_k: int = 5
+    # Neighbor Expansion for fixed_size (ADR-0023); 0/0 = off
+    neighbor_prev: int = 0
+    neighbor_next: int = 0
 
     # LLM generation
     temperature: float = 0.0