feat(theme): add liquid glass themes with visual effects and adaptive compositor support

[Chintanpatel24]

Description

This PR introduces the Liquid Glass theme suite (liquid-dark and liquid-light) inspired by the frosted glass, translucent dark-navy aesthetic of Dolphin with glass effects.

Key Additions & Features

1. New Liquid Themes (liquid-dark.toml & liquid-light.toml):

   • Deep navy-black and frosted light-blue palettes carefully tuned for translucent and glass-effect surfaces.
   • Distinct base, mantle, crust, and surface color steps with vibrant blue accents.

2. Extensible Theme Specification ([effects] section):

   • Added an optional [effects] section to .toml themes allowing any theme to opt into glass styling:
     • sidebar_opacity, content_opacity, toolbar_opacity: granular per-surface opacity control.
     • gradient_enabled, gradient_color, gradient_direction: directional gradient tint overlays on the sidebar and toolbar.
     • glow_enabled, glow_color, glow_radius, glow_opacity: subtle border glow along window and panel edges.
     • blur_enabled, blur_radius: in-app blur effects.
     • noise_enabled, noise_opacity: frosted glass grain texture overlay via Canvas.
     • saturation: glass vibrancy multiplier.
     • refraction_enabled, refraction_strength: glass distortion hint.

3. Backend & ThemeLoader Enhancement (src/services/themeloader.*):

   • Parsed optional [effects] table in ThemeLoader with bounds-checking and zero/off defaults for 100% backward compatibility with existing themes.
   • Exposed all effect properties via Qt properties and signals.
   • Added compositorBlurAvailable property and signal for adaptive compositor awareness.

4. Compositor Awareness (src/main.cpp & Theme.qml):

   • Automatically detects whether the compositor provides blur behind the window (KWindowEffects::BlurBehind).
   • Adapts QML blur intensity accordingly (compositor handles background blur; QML reduces overhead).

5. Settings Panel Integration (src/qml/components/SettingsPanel.qml):

   • Added a dedicated Glass Effects subsection under Look & Feel with live sliders for sidebar/content/toolbar opacity, blur radius, glow intensity & radius, noise grain, saturation, and refraction.
   • Conditionally displayed only when the active theme specifies [effects].
   • Automatically pairs liquid-dark and liquid-light when toggling Dark Mode.

6. Automated Testing:

   • Added comprehensive unit tests in tests/tst_themeloader.cpp testing theme loading, effect property values, fallback behavior on standard themes, and compositor property reactivity.

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[Chintanpatel24]

there's no glsl shaders so it will either depends on lniri or god