Make start_database Hybrid-Aware

The start_database tool is not hybrid-aware. It doesn't check if a ChromaDB instance is already running on the target port before attempting to spawn a new one. This needs to be corrected to support developers who prefer to manage the DB process manually.

Acceptance Criteria

1. The knowledgeBase object in ai/mcp/server/config.mjs is updated with host and port properties.
2. The start_database function in knowledge-base/services/databaseLifecycleService.mjs is updated.
3. It first performs a heartbeat check on the configured host and port.
4. If the heartbeat is successful, it returns a status indicating the database is already running and does not spawn a new process.
5. If the heartbeat fails, it proceeds with spawning a new background process.