Create task event

Create a new task event to track user interactions and system events during annotation.

This endpoint is designed to receive events from the frontend labeling interface to enable
accurate lead time calculation and detailed annotation analytics.

## Event Types

**Core Annotation Events:**
- `annotation_loaded` - When annotation interface is loaded
- `annotation_created` - When annotation is submitted
- `annotation_updated` - When annotation is modified
- `annotation_reviewed` - When annotation is reviewed

**User Activity Events:**
- `visibility_change` - When page visibility changes (tab switch, minimize)
- `idle_detected` - When user goes idle
- `idle_resumed` - When user returns from idle

**Interaction Events:**
- `region_finished_drawing` - When annotation region is completed
- `region_deleted` - When annotation regions are removed
- `hotkey_pressed` - When keyboard shortcuts are used

**Media Events:**
- `video_playback_start/end` - Video playback control
- `audio_playback_start/end` - Audio playback control
- `video_scrub` - Video timeline scrubbing

## Usage

Events are automatically associated with the task specified in the URL path.
The current user is automatically set as the actor. Project and organization
are derived from the task context.

## Example Request

```json
{
    "event_key": "annotation_loaded",
    "event_time": "2024-01-15T10:30:00Z",
    "annotation": 123,
    "meta": {
        "annotation_count": 5,
        "estimated_time": 300
    }
}
```