refactor: move model info to constants

- Added EMBEDDING_MODEL and RERANKER_MODEL to `constants.ts`.
- Updated imports to use these constants in `agent.ts`, `agent_tools/reranker.ts`, and `setup/ingest.ts`.
- Replaced hard‑coded model strings with the new constants for Ollama embeddings and reranker.

constants.ts

@@ -2,3 +2,7 @@ export const STORAGE_DIR = "./storage";
 export const SPEC_DIR = "./spec-built/multipage";
 export const CODE_DIR = "./engine262/src";
 export const GRAPH_FILE = "./graphology/graph.json";
+
+// Model configurations
+export const EMBEDDING_MODEL = "qwen3-embedding:0.6b";
+export const RERANKER_MODEL = "dengcao/Qwen3-Reranker-0.6B:Q8_0";