fix(rag): Final RAG stability and status fixes

- Corrected GeminiEmbeddingProvider model name to gemini-embedding-001.
- Prevented _fetch_models from overwriting active i_status (sending/done/error).
- Updated 	est_rag_engine.py to correctly patch the lazy-loaded chromadb getter.
- Adjusted RAG simulation tests to account for the new initializing... status and automatic initial indexing.
- Fixed typo in 	est_z_negative_flows.py.

tests/test_rag_visual_sim.py

@@ -29,7 +29,7 @@ def test_rag_full_lifecycle_sim(live_gui):
   
   # 3. Verify initial status
   status = client.get_value('rag_status')
-  assert status in ['idle', 'ready'], f"Unexpected initial status: {status}"
+  assert status in ['idle', 'ready', 'initializing...'], f"Unexpected initial status: {status}"
   
   # 4. Trigger Rebuild Index
   print("[SIM] Triggering index rebuild...")