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/darkgreen/hard/dark.txt

@@ -4,7 +4,7 @@ tertiary_paletteKeyColor 376942
 neutral_paletteKeyColor 1E1E26
 neutral_variant_paletteKeyColor 23252D
 background 23262D
-onBackground 02200B
+onBackground F5F5F6
 surface 050505
 surfaceDim 1E1E24
 surfaceBright 1E1E24
@@ -82,6 +82,16 @@ sky cefb97
 sapphire 85ef77
 blue 65eea0
 lavender 90f79e
+klink 65eea0
+klinkSelection 65eea0
+kvisited 73fa90
+kvisitedSelection 73fa90
+knegative 8affab
+knegativeSelection 8affab
+kneutral d0f9f4
+kneutralSelection d0f9f4
+kpositive 8af797
+kpositiveSelection 8af797
 text e0e3e4
 subtext1 bec8cc
 subtext0 889296

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

@@ -4,7 +4,7 @@ tertiary_paletteKeyColor 376942
 neutral_paletteKeyColor 1E1E26
 neutral_variant_paletteKeyColor 23252D
 background 23262D
-onBackground 02200B
+onBackground F5F5F6
 surface 1E1E24
 surfaceDim 1E1E24
 surfaceBright 1E1E24
@@ -82,6 +82,16 @@ sky cefb97
 sapphire 85ef77
 blue 65eea0
 lavender 90f79e
+klink 65eea0
+klinkSelection 65eea0
+kvisited 73fa90
+kvisitedSelection 73fa90
+knegative 8affab
+knegativeSelection 8affab
+kneutral d0f9f4
+kneutralSelection d0f9f4
+kpositive 8af797
+kpositiveSelection 8af797
 text e0e3e4
 subtext1 bec8cc
 subtext0 889296