feat(GUI): add customizable temperature-curve fan control mode

[3Mker]

Introduce a new “Curve” mode that lets users draw and apply custom GPU/CPU temperature-to-fan-speed curves:
• In [AppGUI.py]
– Embed a TemperatureCurve widget with a selector to switch between GPU and CPU curves
– Show/hide the curve editor when entering/exiting Curve mode
– Persist curve points in QSettings (serialize/deserialize)
– On each update tick or mode switch, look up the current temperature on the drawn curve and set the fan speed accordingly

• In TemperatureCurve.py
– Expose APIs to render an interactive point-editing chart
– Provide get_fan_speed_for_temp() to map a temperature value to a fan-speed percentage

• In SettingsKey enum
– Add keys for storing GPUCurvePoints and CPUCurvePoints

No existing fan-control logic was removed—Curve mode simply augments the Custom mode path. All new code is covered by manual verification and preserves backward compatibility with existing modes.

[AlexIII]

Hi! Thank you very much for the contribution! Very nice feature, putting your PR on my task list.

[AlexIII]

A few problems:

1. When I switch to CPU curve and then back to GPU the window suddenly changes in height. We need to set the curve plot height to a fixed value.
2. Axis labels ("Fun speed", "Temperature") and point labels are falling out from the container boundaries. (This is probably due to the hard-coded margins in pixels that do not account for system display scale setting)

Recording.2025-05-24.143333.mp4