### Description
Fixes three issues with the `ntfy` notification provider to improve mobile delivery and readability.
**Previous Behavior:**
1. **Silent Delivery:** Priority was hardcoded to `1` (Min). On Android and iOS, priority 1 notifications are delivered completely silently (no sound, no vibration, hidden from lock screen).
2. **Malformed Payload:** The `payload.data` object was appended as a raw, stringified JSON blob, making the notification body difficult to read.
3. **Tag Fallthrough:** The chained ternary logic for tags caused `error` level events to fall through to the default `information_source` icon.
### Changes Made
- **Dynamic Priority Mapping:** Added `getPriority` to map severity levels to Ntfy's 1-5 scale. `info`/default maps to `2` (quiet ping), `warning` to `3` (default alert), `error` to `4` (high), and `critical` to `5` (max).
- **Plain Text Data Formatting:** Added `formatData` to parse the JSON payload into a clean `- key: value` list. Markdown was purposely avoided to ensure clean rendering in mobile OS lock screen previews.
- **Improved Tagging:** Refactored into a `getTags` helper. Added a base `floppy_disk` icon to instantly identify the notifications, and properly mapped `error` payloads to the `x` icon.
### Related Issues
None (Direct Fix)
