Initial systant implementation in Bun/TypeScript

A lightweight system monitoring agent that:
- Collects metrics via configurable shell commands
- Publishes to MQTT with Home Assistant auto-discovery
- Supports entity types: sensor, binary_sensor, light, switch, button
- Responds to commands over MQTT for controllable entities

Architecture:
- src/config.ts: TOML config loading and validation
- src/mqtt.ts: MQTT client with HA discovery
- src/entities.ts: Entity state polling and command handling
- index.ts: CLI entry point (run, check, once commands)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,46 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# Dependencies
+node_modules
+.pnp
+.pnp.js
+
+# Local env files
+.env
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+# Testing
+coverage
+
+# Turbo
+.turbo
+
+# Vercel
+.vercel
+
+# Build Outputs
+.next/
+out/
+build
+dist
+
+
+# Debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Misc
+.DS_Store
+*.pem
+auth_failures.log
+
+# Nix
+.direnv
+.direnv/*
+
+# Local config (use systant.toml.example as template)
+systant.toml