feat: Add Essentia service to dev workflow and document commands

Commit notes

- Added essentia to dev:services script (starts with other services) - Added dev:services:core for starting without Essentia (lightweight) - Added dedicated Essentia commands: essentia:up, essentia:logs, essentia:build, essentia:health - Updated AGENTS.md with Essentia service URL and commands

To run Essentia: bun run dev:services # Starts all services including Essentia bun run essentia:health # Check if Essentia is running

Co-authored-by: armin.naimi <[email redacted]>