feat(ui): add configurable font colour with UI theme fallback

[BorisKonstantinov]

Heya!

My UI theme settings made it so the app was placing a dark font colour onto my dark taskbars, so Iv implemented the option to change from the UI-matching default to any html colour. Iv made it to change not just the compact representation but the full one as well, as I thought someone might like to have a fancy colour in their setup. More technical notes below. This is fully backward compatible, users who don't touch the setting will never notice a change.

Changes

  contents/config/main.xml
  Two new config entries are added to the General group:
  - fontColourMode (int, default 0) — tracks whether the user has selected UI Theme (0) or Custom (1)
  - fontColour (string, default "") — stores the user-supplied HTML colour value

  contents/ui/GeneralConfig.qml
  A new Font Colour section is appended to the settings form, following the existing field conventions:
  - A ComboBox presenting "UI Theme" and "Custom" options, wired through a QtObject to persist the
  selection
  - A TextField that appears only when "Custom" is selected, with a placeholderText of #ffffff to
  communicate the expected input format. Width matches the existing Latitude/Longitude fields.

  contents/ui/CompactRepresentation.qml
  Three properties are added at the top of the item:
  property int fontColourMode: Plasmoid.configuration.fontColourMode
  property string fontColour: Plasmoid.configuration.fontColour
  readonly property color effectiveFontColour: (fontColourMode === 1 && fontColour !== "") ? fontColour :
   PlasmaCore.Theme.textColor
  All 5 labels (temperature value, unit suffix, and short weather description — in both horizontal and
  vertical panel orientations) are updated from PlasmaCore.Theme.textColor or no explicit colour to
  effectiveFontColour.

  contents/ui/FullRepresentation.qml
  The same three properties and resolution logic are added. A previously missing import
  org.kde.plasma.core as PlasmaCore is also added, which was required for the theme colour fallback. All
  6 labels in the expanded popup view are updated: current temperature, long weather description, rain
  probability, forecast day names, and forecast max/min temperatures. The existing opacity: .5 on the
  minimum temperature label is preserved.

Behaviour

  - With "UI Theme" selected (default), all labels behave exactly as before — no visual change for
  existing users.
  - With "Custom" selected and a valid HTML colour entered, all visible text across both the compact
  panel view and the expanded popup adopts that colour reactively, without requiring a widget restart.
  - If "Custom" is selected but the field is left empty, the widget silently falls back to the theme
  colour.

[Nicolas-Gth]

Oh, I guess this would fix #10 (comment)

[BorisKonstantinov]

@Nicolas-Gth Do you know if I can tag the issue in my commit?

[Nicolas-Gth]

I think only the owner of the repo can do that

[xcurx]

I hope this will be merged soon