Gauge widget displays min value instead of "no data" indicator when no input data is inject at startup

### Description

## Current Behavior
Currently, the Gauge widget initially sets itself to the `min` value if it hasn't received any data at startup. This may create confusion for users because the widget displays a specific value even though there is no data at the input.

**Example of the problem:**
- Gauge configured with `min: 8`
- At dashboard startup, before any input, the widget displays the configured min value of 8
- User sees "8V" and thinks it's an actual measured value
- In reality, there is no data at the input

This is particularly problematic in monitoring applications where it's critical to distinguish between actual measured values and "no data" states.

## Proposed solution
When the Gauge widget has not received any data in its initial state, it would be helpful if it could display an indicator that clearly shows "no data" or "-" rather than defaulting to the minimum value.
Or dropdown with few options:
- "-"
- "n/a"
- "min values"
- "some custom text"

**Environment**
- Dashboard version: v1.29.0
- Node-RED version: v4.1.1

### Have you provided an initial effort estimate for this issue?

I am no FlowFuse team member