feat: thunar & papirus-folders theming + new schemes (#80)

* feat: GTK app theming system

- Implemented custom.css import for user-managed app themes
- process_app_themes() to dynamically update colors in imported CSS files
- Inline comment markers for color replacement (e.g, /* accent-color */)
- Papirus icon color syncing with weighted hue/saturation algorithm

This allows users to create modular app themes that automatically update when the scheme/wallpaper changes

Example usage:
  .app .element { color: #24BD5C; /* accent-color */ }
  .app .element:hover { background: rgba(36, 189, 92, 0.15); /* accent-color with 15% opacity */ }

* feat: atomic theme changes with locking and mode-specific CSS

- Implemented locking to prevent concurrent theme changes
- Added mode-light/mode-dark CSS markers for dynamic property reordering
- Made terminal writes and Papirus sync non-blocking to prevent hangs
- Only save scheme.json after successful theme application

Fixes race conditions during rapid theme switching and ensures Shell and GTK apps scheme stay in sync.

* theme: added to color mapping for custom theming, new schemes

* theme: quick fixes, cleanup

* theme: include thunar.css as template, with new theming system

* theme: modified GTK theming approach

- Dropped comment targeted theming in favor for existing {{  }} replacement
- [app].css.template file created for customization, bypassing built in default if present
- Handling *.template for added templates to be parsed and added to import

* theme: fixes for  thunar.css

* theme: remove .template file use

* theme: path button color adjustment, non-active hover

* fixes & cleanup

* thunar css fixes

* more css fixes

* format

* fix tab vert spacing

---------

Co-authored-by: 2 * r + 2 * t <61896496+soramanew@users.noreply.github.com>

src/caelestia/data/schemes/dracula/medium/dark.txt

@@ -0,0 +1,110 @@
+primary_paletteKeyColor BD93F9
+secondary_paletteKeyColor 50FA7B
+tertiary_paletteKeyColor FF79C6
+neutral_paletteKeyColor 282A36
+neutral_variant_paletteKeyColor 44475A
+background 282A36
+onBackground F8F8F2
+surface 343746
+surfaceDim 21222C
+surfaceBright 4D4F66
+surfaceContainerLowest 191A21
+surfaceContainerLow 3C3F4E
+surfaceContainer 3E4153
+surfaceContainerHigh 4D4F66
+surfaceContainerHighest 565970
+onSurface F8F8F2
+surfaceVariant 3E4153
+onSurfaceVariant F8F8F2
+inverseSurface F8F8F2
+inverseOnSurface 282A36
+outline 6272A4
+outlineVariant 4D4F66
+shadow 000000
+scrim 000000
+surfaceTint BD93F9
+primary BD93F9
+onPrimary 282A36
+primaryContainer 4D4F66
+onPrimaryContainer BD93F9
+inversePrimary 9D73D9
+secondary 50FA7B
+onSecondary 282A36
+secondaryContainer 4D4F66
+onSecondaryContainer 50FA7B
+tertiary FF79C6
+onTertiary 282A36
+tertiaryContainer 4D4F66
+onTertiaryContainer FF79C6
+error FF5555
+onError 282A36
+errorContainer 4C3743
+onErrorContainer FF5555
+primaryFixed BD93F9
+primaryFixedDim 9D73D9
+onPrimaryFixed 282A36
+onPrimaryFixedVariant 3E4153
+secondaryFixed 50FA7B
+secondaryFixedDim 30DA5B
+onSecondaryFixed 282A36
+onSecondaryFixedVariant 3E4153
+tertiaryFixed FF79C6
+tertiaryFixedDim DF59A6
+onTertiaryFixed 282A36
+onTertiaryFixedVariant 3E4153
+term0 282A36
+term1 FF5555
+term2 50FA7B
+term3 F1FA8C
+term4 BD93F9
+term5 FF79C6
+term6 8BE9FD
+term7 F8F8F2
+term8 6272A4
+term9 FF6E6E
+term10 69FF94
+term11 FFFFA5
+term12 D6ACFF
+term13 FF92DF
+term14 A4FFFF
+term15 FFFFFF
+rosewater F8F8F2
+flamingo FFB86C
+pink FF79C6
+mauve BD93F9
+red FF5555
+maroon FF6E6E
+peach FFB86C
+yellow F1FA8C
+green 50FA7B
+teal 8BE9FD
+sky 8BE9FD
+sapphire 8BE9FD
+blue BD93F9
+lavender BD93F9
+klink BD93F9
+klinkSelection BD93F9
+kvisited FF79C6
+kvisitedSelection FF79C6
+knegative FF5555
+knegativeSelection FF5555
+kneutral F1FA8C
+kneutralSelection F1FA8C
+kpositive 50FA7B
+kpositiveSelection 50FA7B
+text F8F8F2
+subtext1 F8F8F2
+subtext0 E6E6E6
+overlay2 A0A0A0
+overlay1 8A8A8A
+overlay0 6272A4
+surface2 3E4153
+surface1 343746
+surface0 282A36
+base 282A36
+mantle 21222C
+crust 191A21
+success 50FA7B
+onSuccess 282A36
+successContainer 4D4F66
+onSuccessContainer F8F8F2