Real-time SSE event stream in the odio API

All backends push state changes as Server-Sent Events (SSE). Connect once and get a unified stream of everything happening on the node.

Endpoint

GET /events

Parameter	Description	Example
`backend`	Only receive events from this backend	`?backend=mpris`
`types`	Only receive these event types	`?types=player.updated,player.added`
`exclude`	Exclude these event types	`?exclude=player.position`
`keepalive`	Keepalive interval	`?keepalive=30s`

Event	Backend	Trigger
`player.updated`	mpris	Playback state, volume, or metadata change
`player.added`	mpris	New player appeared
`player.removed`	mpris	Player closed
`player.position`	mpris	Periodic position tick
`player.tracklist.updated`	mpris	Tracklist replaced, or a track added, removed, or its metadata changed
`audio.updated`	pulseaudio	Sink input added or changed
`audio.removed`	pulseaudio	Sink input removed
`service.updated`	systemd	Unit state change
`bluetooth.updated`	bluetooth	Adapter or device state change
`power.action`	power	Reboot or power-off triggered
`upgrade.info`	upgrade	Detector status changed, or upgrade run lifecycle
`upgrade.progress`	upgrade	Live progress line from a running upgrade