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>

.env.example

@@ -5,12 +5,18 @@ OPENAI_API_KEY=sk-...
 QDRANT_URL=http://localhost:6333
 QDRANT_API_KEY=
 
-# Fixed models (not configurable per strategy)
-EMBEDDING_MODEL=text-embedding-3-small
+# Default cloud Embedding Model (registry id / OpenAI model name)
+EMBEDDING_MODEL=text-embedding-3-large
 LLM_MODEL=gpt-4o-mini
 
+# Local Ollama embeddings (Active model switched in Admin)
+OLLAMA_BASE_URL=http://192.168.10.10:11435
+
 # Retrieval defaults
 TOP_K=5
+# Neighbor Expansion for fixed_size only (ADR-0023); 0 = off
+NEIGHBOR_PREV=0
+NEIGHBOR_NEXT=0
 
 # LLM generation parameters
 TEMPERATURE=0.0