fix: sanitize ChromaDB URL and update docker-compose CORS config

- src/semantic-cache.ts: Add robust URL sanitization in initialize().
  Trim whitespace and reject malformed URLs (e.g. empty host like
  'http://:8666') before passing to ChromaClient.

- src/main.ts: Validate ChromaDB URL in the settings tab onChange.
  Fall back to 'http://localhost:8000' if the value is empty or lacks
  '://'.

- docker-compose.yml: Add CHROMA_SERVER_CORS_ALLOW_ORIGINS=["*"] to
  allow cross-origin requests from Obsidian's app://obsidian.md origin.

docker-compose.yml

@@ -2,10 +2,11 @@ services:
   chroma:
     image: chromadb/chroma:latest
     ports:
-      - "8666:8000"
+      - '8666:8000'
     environment:
       - CHROMA_SERVER_HOST=0.0.0.0
       - CHROMA_SERVER_HTTP_PORT=8000
+      - CHROMA_SERVER_CORS_ALLOW_ORIGINS=["*"]
     volumes:
       - chroma_data:/chroma/chroma
     restart: unless-stopped